Operating with multiple schedulers in a wireless system

ABSTRACT

Systems and methods are disclosed for a WTRU to operate using multiple schedulers. The WTRU may exchange data with the network over more than one data path, such that each data path may use a radio interface connected to a different network node and each node may be associated with an independent scheduler. For example, a WTRU may establish a RRC connection between the WTRU and a network. The RRC connection may establish a first radio interface between the WTRU and a first serving site of the network and a second radio interface between the WTRU and a second serving site of the network. The RRC connection may be established between the WTRU and the MeNB and a control function may be established between the WTRU and the SCeNB. The WTRU may receive data from the network over the first radio interface or the second radio interface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 14/794,493, filed on Jul. 8, 2015, which is acontinuation of U.S. Non-Provisional patent application Ser. No.13/974,946, filed on Aug. 23, 2013, which issued as U.S. Pat. No.9,113,450 on Aug. 18, 2015, which claims the benefit of U.S. ProvisionalPatent Application No. 61/692,548, filed Aug. 23, 2012; U.S. ProvisionalPatent Application No. 61/726,448, filed Nov. 14, 2012; U.S. ProvisionalPatent Application No. 61/753,323, filed Jan. 16, 2013; U.S. ProvisionalPatent Application No. 61/753,334, filed Jan. 16, 2013; U.S. ProvisionalPatent Application No. 61/821,071, filed May 8, 2013; U.S. ProvisionalPatent Application No. 61/821,186, filed May 8, 2013; and U.S.Provisional Patent Application No. 61/863,311, filed Aug. 7, 2013, thecontents of which are hereby incorporated by reference in theirentirety.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, etc. These systemmay be multiple-access systems capable of supporting communication withmultiple user by sharing the available system resources (e.g.,bandwidth, transmit power, etc.). Examples of such multiple-accesssystems may include code division multiple access (CDMA) systems,wideband code division multiple access (WCDMA) systems, time divisionmultiple access (TDMA) systems, frequency division multiple access(FDMA) systems, the Third Generation Partnership Project (3GPP) LongTerm Evolution (LTE) systems, and orthogonal frequency division multipleaccess (OFDMA) systems, etc.

These multiple access technologies have been adopted to provide a commonprotocol that enables different wireless devices to communicate onmunicipal, national, regional, and even the global level. An example ofan emerging telecommunication standard is LTE. LTE is a set ofenhancements to the Universal Mobile Telecommunications System (UMTS)mobile standard promulgated by 3GPP. LTE is designed to better supportmobile broadband Internet access by improving spectral efficiency,lowering costs, improving services, making use of new spectrum, andbetter integrating with other open standards using OFDMA on the downlink(DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output(MIMO) antenna technology.

SUMMARY

Systems and methods are disclosed for a wireless transmit/receive unit(WTRU) to operate in a wireless communication systems that utilizesmultiple schedulers. For example, in some multiple scheduler systems,the schedulers may lack a low latency communication interface forcoordinating scheduling operation associated with the same WTRU. TheWTRU may exchange data with the network over more than one data path,such that each data path may use a radio interface connected to adifferent network node and each node may be associated with anindependent scheduler. For example, a WTRU may establish a radioresource control (RRC) connection between the WTRU and a network. TheRRC connection may establish a first radio interface between the WTRUand a first serving site of the network and a second radio interfacebetween the WTRU and a second serving site of the network. The firstserving site may be a Macro eNodeB (MeNB) and the second serving sitemay be a Small Cell eNodeB (SCeNB). The RRC connection may beestablished between the WTRU and the MeNB and a control function may beestablished between the WTRU and the SCeNB. The WTRU may receive datafrom the network over the first radio interface or the second radiointerface.

As an example, methods and systems are described WTRU to operate usingmultiple layers that are independently scheduled. For example, the WTRUmay establish a radio resource control (RRC) connection with a firstserving site. The WTRU may receive a reconfiguration message from thefirst serving site. The reconfiguration message may include aconfiguration for the WTRU to connect to one or more cells associatedwith a second serving site. The reconfiguration message may indicate atleast one radio bearer (RB) to be used by the WTRU at the second servingsite. The WTRU may determine to activate a connection to the secondserving site. The WTRU may monitor a control channel of at least one ofthe one or more cells associated with the second serving site based ondetermining activate the connection to the second serving site. Forexample, the reconfiguration message may be an RRC connectionreconfiguration message, and the at least one RB may be a new RBestablished for use at the second serving site. In an example, thereconfiguration message may be an RRC connection reconfiguration messagethat includes a mobility control information element, the at least oneRB may be an RB that was previously mapped to the first serving site,and the RRC connection reconfiguration message may trigger the WTRU tobegin associating the RB that was previously mapped to the first servingsite with the second serving site.

In an example, the reconfiguration message may include a plurality ofradio resource management (RRM) configurations for a given cellassociated with the second serving site. Upon activating the connectionto the second serving site, the WTRU may apply a default RRMconfiguration of the plurality of RRM configurations. The WTRU mayreceive one or more of physical layer signaling or layer 2 signaling.The one or more of physical layer signaling or layer 2 signaling may beindicative of another RRM configuration of the plurality of RRMconfigurations that the WTRU should apply at the given cell of thesecond serving site. The WTRU may then apply the another RRMconfiguration when connected to the given cell of the second servingsite. For example, the one or more of physical layer signaling or layer2 signaling may include one or more of a physical downlink controlchannel (PDCCH) transmission or a medium access control (MAC) controlelement (CE). The WTRU may determine which of the plurality of RRMconfigurations to apply based on an index received in the one or more ofphysical layer signaling or layer 2 signaling. At least one RRMconfiguration of the plurality of RRM configurations may include one ormore of a physical layer configuration, a channel quality indication(CQI) reporting configuration, or a MAC configuration.

In an example, the control plane may be distribute across the servingsites, coordinated between the serving sites, and/or centralized at oneor the serving sites. For example, a network RRC entity associated withboth the first serving site and the second serving site may be locatedat the second serving site. One or more signaling radio bearersterminated at the RRC entity at the first serving site may betransmitted to the WTRU via the second serving site. For example, theone or more signaling radio bearers terminated at the RRC entity at thefirst serving site that are transmitted to the WTRU via the secondserving site may be associated with control information for managing theradio resources between the WTRU and the second serving site. The WTRUmay perform one or more measurements of at least one or the one or morecells associated with the second serving site. The WTRU may report theone or more measurements to the first serving site.

The WTRU may handle security for transmissions associated with the firstserving site and/or the second serving site in a semi-coordinated and/orindependent fashion. For example, each of the first serving site and thesecond serving site may be associated with independent packet dataconvergence protocol (PDCP) instances for the WTRU. The WTRU may beconfigured to utilize the same security key for ciphering PDCP packetsto be sent to either a first PDCP instance associated with the firstserving site or a second PDCP instance associated with the secondserving site. For example, the WTRU may be configured to use a differentBEARER parameter for each of the first PDCP instance associated with thefirst serving site and the second PDCP instance associated with thesecond serving site. For example, a respective BEARER parameter used forciphering transmissions to the second PDCP entity at the second servingsite may be determined based on a layer identity associated with thesecond serving site.

The WTRU may implement two or more sets of protocol stacks for thecontrol plane and/or the data plane. For example, the WTRU may include afirst medium access control (MAC) instance configured to access cellsassociated with the first serving site, and a second MAC instanceconfigured to access cells associated with the second serving site. TheWTRU may be configured to data associated with at least one logicalchannel using either of the first MAC instance or the second MACinstance. The WTRU may be configured to deactivate at least one bearerassociated with the first serving site based on activating theconnection to the second serving site. The WTRU may be configured tomeasure at least one cell associated with the second serving site, anddetermine to autonomously activate the at least one cell based on themeasurements. A RRC reconfiguration message may include apreconfiguration for the at least one cell, and the WTRU may beconfigured to autonomously activate the at least one cell using a randomaccess channel (RACH) procedure.

The RRC connection for the WTRU may establish one or more SRBs betweenthe WTRU and the network, such that each of the established SRBs may beassigned to at least one of the first radio interface and the secondradio interface. A received/transmitted RRC PDU may be associated withone of the one or more SRBs. The RRC PDU may be received over either thefirst radio interface or the second radio interface regardless of itsassociated SRB. The RRC connection may be controlled by the network. TheWTRU may transmit an indication to the network indicating that the WTRUsupports multi-scheduling operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented.

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A.

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A.

FIG. 1D is a system diagram of another example radio access network andanother example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 1E is a system diagram of another example radio access network andanother example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 2A illustrates an example reference architecture that may implementa multi-scheduler architecture.

FIG. 2B illustrates another example reference architecture that mayimplement a multi-scheduler architecture.

FIG. 3 illustrates an example implementation of a centralized controlplane.

FIG. 4 illustrates another example implementation of a centralizedcontrol plane.

FIG. 5 illustrates an example control plane protocol stack for SRBsexchanged via the data path including a MeNB when an RRC instance isterminated at the MeNB on the network side.

FIG. 6 illustrates an example control plane protocol stack for SRBsexchanged via the data path including an SCeNB when an RRC instance isterminated at the MeNB on the network side.

FIG. 7 illustrates an example control plane protocol stack for acoordinated control plane where a first RRC instance is terminated at afirst serving site and a second RRC instance is terminated at a secondserving site.

FIG. 8 illustrates an example control plane protocol stack for SRBsexchanged via the data path including a first serving site when an RRCinstance is terminated at the first serving site on the network side.

FIG. 9 illustrates an example control plane protocol stack for SRBsexchanged via the data path including a second serving site when an RRCinstance is terminated at the second serving on the network side.

FIG. 10 illustrates an example control plane protocol stack for adistributed control plane where the RRC instance is terminated at firstserving site.

FIG. 11 illustrates an example of a control plan protocol stackcomprising a distributed approach for SRB0, SRB1, and SRB2 of terminatedan RRC instance at a first serving site.

FIG. 12 illustrates an example of a control plane protocol stackcomprising a distributed approach for an SRB associated with a secondserving site.

FIG. 13 illustrates an example protocol stack that may be used for userplane data paths when the data paths are split above the PDCP layer inthe network.

FIG. 14 illustrates an example protocol stack where SRBs may beassociated with a single SAP, and the data paths are split above thePDCP layer in the network using a centralized control plane.

FIG. 15 illustrates an example for a data path split above the PDCPlayer for the user plane where multiple DRB SAPs are utilized.

FIG. 16 illustrates an example protocol stack where SRBs may beassociated with multiple SAPs and the data paths are split above thePDCP layer in the network using a centralized control plane.

FIGS. 17 and 18 are diagrams illustrating examples of user planeprotocol stacks.

FIG. 19 illustrates an example control plane protocol stack of a datapath split above RLC where PDCP PDUs may be transferred over a pluralityof data paths.

FIG. 20 illustrates an example of a data path associated with asecondary layer when the data split occurs below the PDCP layer (e.g.,above the RLC layer).

FIG. 21 illustrates an example control plane protocol stack that may beutilized if the data paths are split above the MAC layer.

FIG. 22 illustrates an example user plane protocol stack that may beutilized if the data paths are split above the MAC layer.

FIG. 23 illustrates an example Layer 2 structure for uplink multi-siteoperation that may implemented a segregated UL transmission scheme.

FIG. 24 illustrates an example Layer 2 structure for uplink multi-siteoperation where a split RLC transmission scheme is utilized.

FIG. 25 illustrates an example Layer 2 structure where a data for agiven logical channel may be mapped to a plurality of transport channelsand the transport channels may be associated with different servingsites.

FIG. 26 illustrates an example of Layer 2 structure for downlinkmulti-site operation that may be used for a segregated DL transmissionscheme.

FIG. 27 illustrates an example of Layer 2 structure for downlinkmulti-site operation that may be used for a split RLC DL transmissionscheme.

FIG. 28 illustrates an example Layer 2 structure where downlink data fora given logical channel may be mapped to a plurality of transportchannels and the transport channels may be associated with differentserving sites.

DETAILED DESCRIPTION

A detailed description of illustrative embodiments will now be describedwith reference to the various Figures. Although this descriptionprovides a detailed example of possible implementations, it should benoted that the details are intended to be exemplary and in no way limitthe scope of the application.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, and/or 102 d (whichgenerally or collectively may be referred to as WTRU 102), a radioaccess network (RAN) 103/104/105, a core network 106/107/109, a publicswitched telephone network (PSTN) 108, the Internet 110, and othernetworks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations, networks,and/or network elements. Each of the WTRUs 102 a, 102 b, 102 c, 102 dmay be any type of device configured to operate and/or communicate in awireless environment. By way of example, the WTRUs 102 a, 102 b, 102 c,102 d may be configured to transmit and/or receive wireless signals andmay include user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106/107/109, theInternet 110, and/or the networks 112. By way of example, the basestations 114 a, 114 b may be a base transceiver station (BTS), a Node-B,an eNode B, a Home Node B, a Home eNode B, a site controller, an accesspoint (AP), a wireless router, and the like. While the base stations 114a, 114 b are each depicted as a single element, it will be appreciatedthat the base stations 114 a, 114 b may include any number ofinterconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 a and/or the base station114 b may be configured to transmit and/or receive wireless signalswithin a particular geographic region, which may be referred to as acell (not shown). The cell may further be divided into cell sectors. Forexample, the cell associated with the base station 114 a may be dividedinto three sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 115/116/117,which may be any suitable wireless communication link (e.g., radiofrequency (RF), microwave, infrared (IR), ultraviolet (UV), visiblelight, etc.). The air interface 115/116/117 may be established using anysuitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, 102 c may implement a radio technology such as UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA),which may establish the air interface 115/116/117 using wideband CDMA(WCDMA). WCDMA may include communication protocols such as High-SpeedPacket Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may includeHigh-Speed Downlink Packet Access (HSDPA) and/or High-Speed UplinkPacket Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface115/116/117 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 (e.g., 802.11ac,802.11af, and the like) to establish a wireless local area network(WLAN). In another embodiment, the base station 114 b and the WTRUs 102c, 102 d may implement a radio technology such as IEEE 802.15 toestablish a wireless personal area network (WPAN). In yet anotherembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayutilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A,etc.) to establish a picocell or femtocell. As shown in FIG. 1A, thebase station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106/107/109.

The RAN 103/104/105 may be in communication with the core network106/107/109, which may be any type of network configured to providevoice, data, applications, and/or voice over internet protocol (VoIP)services to one or more of the WTRUs 102 a, 102 b, 102 c, 102 d. Forexample, the core network 106/107/109 may provide call control, billingservices, mobile location-based services, pre-paid calling, Internetconnectivity, video distribution, etc., and/or perform high-levelsecurity functions, such as user authentication. Although not shown inFIG. 1A, it will be appreciated that the RAN 103/104/105 and/or the corenetwork 106/107/109 may be in direct or indirect communication withother RANs that employ the same RAT as the RAN 103/104/105 or adifferent RAT. For example, in addition to being connected to the RAN103/104/105, which may be utilizing an E-UTRA radio technology, the corenetwork 106/107/109 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d to access the PSTN 108, the Internet 110,and/or other networks 112. The PSTN 108 may include circuit-switchedtelephone networks that provide plain old telephone service (POTS). TheInternet 110 may include a global system of interconnected computernetworks and devices that use common communication protocols, such asthe transmission control protocol (TCP), user datagram protocol (UDP)and the internet protocol (IP) in the TCP/IP internet protocol suite.The networks 112 may include wired or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another core network connected to one or moreRANs, which may employ the same RAT as the RAN 103/104/105 or adifferent RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment. Also, embodiments contemplate that thebase stations 114 a and 114 b, and/or the nodes that base stations 114 aand 114 b may represent, such as but not limited to transceiver station(BTS), a Node-B, a site controller, an access point (AP), a home node-B,an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a homeevolved node-B gateway, and proxy nodes, among others, may include someor all of the elements depicted in FIG. 1B and described herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in one embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In another embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet another embodiment, the transmit/receive element 122 may beconfigured to transmit and receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination implementation while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 103 and the core network 106according to an embodiment. As noted above, the RAN 103 may employ aUTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102 cover the air interface 115. The RAN 103 may also be in communicationwith the core network 106. As shown in FIG. 1C, the RAN 103 may includeNode-Bs 140 a, 140 b, 140 c, which may each include one or moretransceivers for communicating with the WTRUs 102 a, 102 b, 102 c overthe air interface 115. The Node-Bs 140 a, 140 b, 140 c may each beassociated with a particular cell (not shown) within the RAN 103. TheRAN 103 may also include RNCs 142 a, 142 b. It will be appreciated thatthe RAN 103 may include any number of Node-Bs and RNCs while remainingconsistent with an embodiment.

As shown in FIG. 1C, the Node-Bs 140 a, 140 b may be in communicationwith the RNC 142 a. Additionally, the Node-B 140 c may be incommunication with the RNC142 b. The Node-Bs 140 a, 140 b, 140 c maycommunicate with the respective RNCs 142 a, 142 b via an Iub interface.The RNCs 142 a, 142 b may be in communication with one another via anIur interface. Each of the RNCs 142 a, 142 b may be configured tocontrol the respective Node-Bs 140 a, 140 b, 140 c to which it isconnected. In addition, each of the RNCs 142 a, 142 b may be configuredto carry out or support other functionality, such as outer loop powercontrol, load control, admission control, packet scheduling, handovercontrol, macrodiversity, security functions, data encryption, and thelike.

The core network 106 shown in FIG. 1C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between and the WTRUs102 a, 102 b, 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1D is a system diagram of the RAN 104 and the core network 107according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1D, theeNode-Bs 160 a, 160 b, 160 c may communicate with one another over an X2interface.

The core network 107 shown in FIG. 1D may include a mobility managementgateway (MME) 162, a serving gateway 164, and a packet data network(PDN) gateway 166. While each of the foregoing elements are depicted aspart of the core network 107, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 162 may be connected to each of the eNode-Bs 160 a, 160 b, 160 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNode-Bs 160 a,160 b, 160 c in the RAN 104 via the S1 interface. The serving gateway164 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 164 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 164 may also be connected to the PDN gateway 166,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 107 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 107 and the PSTN 108. In addition, the corenetwork 107 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1E is a system diagram of the RAN 105 and the core network 109according to an embodiment. The RAN 105 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 117. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 105, andthe core network 109 may be defined as reference points.

As shown in FIG. 1E, the RAN 105 may include base stations 180 a, 180 b,180 c, and an ASN gateway 182, though it will be appreciated that theRAN 105 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 180 a, 180 b,180 c may each be associated with a particular cell (not shown) in theRAN 105 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 117. In oneembodiment, the base stations 180 a, 180 b, 180 c may implement MIMOtechnology. Thus, the base station 180 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 180 a, 180 b, 180 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 182 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, 102 c and the RAN105 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 109.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 109 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,180 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 180 a, 180 b,180 c and the ASN gateway 182 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 102 c.

As shown in FIG. 1E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 184 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 186 may be responsible for userauthentication and for supporting user services. The gateway 188 mayfacilitate interworking with other networks. For example, the gateway188 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 188 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1E, it will be appreciated that the RAN 105may be connected to other ASNs and the core network 109 may be connectedto other core networks. The communication link between the RAN 105 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 105 and the other ASNs. The communication link betweenthe core network 109 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

Systems and methods are disclosed for utilizing multi-node schedulingwhereby a WTRU may exchange data over a wireless communication networkusing more than one data path. For example, different air interfacetransmission/reception points may be associated with each of the datapaths (e.g., each data path may use a radio interface that is associatedwith a different network node). The different transmission/receptionpoints associated with the different data paths may independentlyschedule WTRU transmissions over their respective data path. In otherwords, a first scheduler may schedule transmissions to/from a WTRU overa first data path, and a second scheduler may schedule transmissionsto/from the WTRU over a second data path. The differenttransmission/reception points within the network may be in communicationwith each other; however, the data links between the differenttransmission/reception points may be associated with a relative highlatency. Therefore, it may be difficult or impractical for the differenttransmission/reception points to schedule transmissions over the datapaths in a coordinated manner. Thus, each transmission/reception pointmay independently schedule the WTRU to transmit and/or receive over arespective transmission path. Such transmission/reception points may bereferred to as serving sites.

The examples described herein may be described in terms of examplesimplemented within an evolved universal terrestrial radio access network(E-UTRAN). However, the methods and systems disclosed herein may beapplicable to other network architectures and/or used by other networknodes. Data that transmitted to (or received from) a serving site for aWTRU may be provided to (passed from) a core network (e.g., a servinggateway (S-GW)). A serving site may support one or more Layer 2protocols (e.g., MAC, RLC and/or PDCP) for a given radio bearer.

For example, a WTRU may establish a radio resource control (RRC)connection between the WTRU and a wireless communication network. TheRRC connection may establish or configure a first radio interfacebetween the WTRU and a first node of the network and a second radiointerface between the WTRU and a second node of the network. The firstnode may be a Macro eNodeB (MeNB) and the second node may be a SmallCell eNodeB (SCeNB). In an example, the RRC connection may beestablished between the WTRU and the MeNB and a control function may beestablished between the WTRU and the SCeNB. The WTRU may receive datafrom the network over the first radio interface and/or the second radiointerface. Although the examples described herein may be described withrespect to operation utilizing a first data path (e.g., may also bereferred to as a first layer, a primary data path, a primary layer,etc.) that is associated with a MeNB and a second data path (e.g., mayalso be referred to as a second layer, a secondary data path, asecondary layer, etc.), the methods and systems described herein may beequally applicable to other network transmission/reception points thatare independently scheduled (e.g., two or more independently scheduledeNBs, two or more independently scheduled NBs, two or more independentlyscheduled RAN access nodes, etc.).

The systems and methods described herein may be applicable to one ormore multi-scheduler frameworks wherein different network nodes serve astransmission/reception points for different data paths. The use ofmultiple data paths may be facilitated by decoupling the relationshipbetween bearers, radio bearers, and/or the like. For example, when amulti-scheduler framework is utilized, an evolved packet service (EPS)bearer may be associated with multiple radio bearers. Whenmulti-scheduler operation is utilized, the WTRU may be configured toexchange control signaling and/or user plane data over one or more datapaths.

A data path may be defined based on the identity of one or more serviceaccess points (SAPs) that are used to transmit data associated with thedata path, based on the identity of one or more network interfaces ornodes that are used to transmit the data associated with the data path,based on one or more radio interfaces (e.g., X2, X2bis, X2′, Uu, etc.)that are used to transmit data associated with the data path, and/or thelike. Further, a data path may be defined based on the communicationprotocol stack (e.g., including one or more of a packet data convergenceprotocol (PDCP) layer, a radio link control (RLC) layer, a medium accesscontrol (MAC) layer, a physical (PHY) layer, etc.) that may be used todefine a processing sequence for transferring information associatedwith the data path. The information or data transmitted over a data pathmay include one or more of control plane data (e.g., non-access stratum(NAS) signaling, RRC signaling, etc.) and/or user plane data (e.g., IPpackets, etc.). Data paths may be independently scheduled from otherdata paths.

For example, in LTE Release 11, data transfer may be performed over asingle data path between the WTRU and the network. For the controlplane, there may be a direct mapping between an SRB and a LogicalChannel (LCH) over a single Uu interface (e.g., an interface between theWTRU and an eNB). For the user plane, there may be a direct mappingbetween an EPS bearer, a Data Radio Bearer (DRB), and a Logical Channel(LCH) over that same Uu interface.

However, in the presence of multiple independent schedulers, the WTRUmay be configured to utilize more than one data path, for example whereeach data path may be established between the WTRU and network nodesusing different Uu interfaces. A data path may also be referred to as alayer. For example, the WTRU may be configured to transmit and/orreceive data over multiple layers, where each layer is associated with adifferent data path. Each layer may be scheduled independently of otherlayers. Each layer may be associated with a different air interface forthe WTRU. Each layer may be associated with a serving site that servesas a transmission and/or reception point for the data path within thenetwork.

In order to support transmissions over multiple layers, a plurality ofMAC instances may be established at the WTRU. For example, the WTRU maybe configured with multiple MAC instances that are each associated witha corresponding set of physical layer parameters and/or withlayer-specific radio bearers. As an example, the WTRU may be configuredwith a set of primary layer information (e.g., which may be associatedwith a macro layer/MeNB/macro serving site) and one or more sets ofsecondary layer information (e.g., which may be associated with a smallcell layer/SCeNB/small cell serving site). A WTRU may be configured withone or more serving cells for each layer. For example, the WTRU mayperform carrier aggregation in each of the layers such thattransmissions and/or reception may occur from multiple cells within agiven layer.

For example, the WTRU may be configured to operate with one or moreserving sites (e.g., also referred to as serving eNBs) in the downlinkand/or the uplink. Each serving site may be associated with one or moreserving cells. For example, a WTRU may operate using a single servingcell (e.g., component carrier) at first serving site (e.g., a MeNB) andmay operate using a plurality of serving cells (e.g., a plurality ofcomponent carriers) at a second serving site (e.g., a SCeNB). Thus, aserving site may be associated with a plurality of serving cells. Eachserving cell of a given serving site may be configured for operation ata corresponding component carrier (CC). A serving site may support oneor multiple CCs. Each CC within a serving site may operate using adifferent frequency range than other CCs of the serving site, so thateach of the serving cells associated with a given serving site may betransmitted using a different CC. However, serving cells from differentserving sites may be transmitted using the same CC. Therefore, servingcells may be associated with the same CC but with different servingsites. A WTRU may be configured with a maximum number of serving sitesover which the WTRU may operate (e.g., 1, 2, 3, 4, etc.). An indicationof the maximum number of serving sites that the WTRU may be allowed toutilize may be signaled by the WTRU to the network as part of WTRUcapability information and/or may be determined by the network based onthe operating class of a WTRU.

A serving site may be associated with one or more Transport Channels.For example, in the uplink the WTRU may be configured to deliver data tothe physical layer using a transport channel (e.g., UL-SCH) that isassociated with a serving cell associated with a specific serving site.In an example, each transport channel may be specific to a given servingsite/layer, although the transport channel may be associated withmultiple serving cells and/or component carriers within that servingsite. For example, a UL-SCH may be associated with a specific servingsite (e.g., a serving site associated with the data path including theMeNB) and one or more component carriers associated with that servingsite (e.g., multiple component carriers that are associated with theMeNB). A transport block to be delivered to that serving site may beserved with data associated with the transport channel mapped to thatserving site. In the downlink the WTRU may be configured to receive datato at the physical layer and deliver the data to a transport channel(e.g., DL-SCH) that is associated with a serving cell associated with aspecific serving site. For example, a DL-SCH may be associated with aspecific serving site (e.g., a serving site associated with the datapath including the SCeNB) and one or more component carriers associatedwith that serving site (e.g., multiple component carriers that areassociated with the SCeNB). A transport block received at the physicallayer may be mapped to a transport channel associated with that servingsite from which the transport block was received. A given serving sitemay be associated with zero, one, or more than one UL-SCHs and zero,one, or more than one DL-SCHs.

Each serving site may be associated with a corresponding MAC instance atthe WTRU. The WTRU may be configured with multiple MAC instances. EachMAC instance may be associated with a specific serving site. The termsserving site, layer, data path, MAC instance, etc. may be usedinterchangeably herein. Each MAC instance may be associated with one ormore configured serving cells and support one or more CCs. Each UL-SCHand/or DL-SCH may be associated with a given MAC instance (e.g., aone-to-one instance between a transport channel and a MAC instance).

A MAC instance may be configured with a Primary Cell (PCell). For eachserving site (and/or MAC instance), one of its associated serving cellsmay support at least a subset of the functionality supported by aprimary serving cell (PcCell) in legacy (e.g., single-site) systems. Forexample, one or more of the serving cells of a given MAC instance maysupport PUCCH transmissions that may be utilized for sending schedulingrequests, HARQ feedback, CSI feedback, and/or the like related to theUL-SCH and/or the DL-SCH mapped to the corresponding serving site. Aserving cell that is configured to receive uplink control information(UCI) associated with the transport channels of the serving site may bereferred to as a “site PCell” and/or a “MAC primary cell.” Each MACinstance may be configured with one PCell and zero or more SCells.Further, the PCell of a primary MAC instance (e.g., the MAC instanceassociated with a MeNB) may have additional functionality specific tothat MAC instance. A serving site may be associated with a data path. Aserving site may correspond to a single data path.

RRC may utilized to configure multiple MAC instances. For example, whenRRC configures a MAC instance for operation, the WTRU may determinewhether a received configuration or parameter is associated with givenMAC instance based on an explicit indication included in a field of theinformation element (IE) that includes the configuration information. Inan example, is multiple configurations are received, the WTRU mayimplicitly determine that each configuration applies to respective MACinstance. For example, if multiple radioResourceConfigDedicated IEs arereceived in a RRC connection setup/modification message, then the WTRUmay determine that a first radioResourceConfigDedicated IE is associatedwith a first MAC instance and that a second radioResourceConfigDedicatedIE is associated with a second MAC instance. In an example, differenttypes of IEs may be defined for configuring a secondary MAC instance(e.g., a radioResourceConfigDedicatedSecondaryMACInstance IE). The WTRUmay determine that a received configuration/IE applies to a secondaryMAC instance based on the type of the IE that is received. The WTRU maydetermine that a received configuration/IE applies to a secondary MACinstance based on the presence of an access-stratum (AS) configurationin the IE (e.g., similar to the mobilityControl IE). For example, ifcertain AS configuration information is present in receivedconfiguration information, the WTRU may determine that the configurationapplies to a secondary MAC instance. If the AS configuration informationis absent in received configuration information, the WTRU may determinethat the configuration applies to a primary MAC instance. The WTRU maydetermine which MAC instance a given configuration is applicable tobased on the identity of the SRB over which the configuration message isreceived (e.g., SRB3 may indicate configuration information for thesecondary MAC instance), for example if such SRB has been previouslyconfigured for the WTRU. If individual RRC instances/entities areassociated with the different serving sites, then the WTRU may determinewhich MAC instance the configuration applies to based on the RRC entityfrom which the configuration was received.

The different layers utilized by the WTRU may be associated withdifferent types of radio access nodes and/or different types of cells.For example, the primary layer may be associated with a macro cellserved by MeNB and a secondary layer may be associated small cell servedby a SCeNB. The network arrangement may be transparent to the WTRU.Although examples may be described where the schedulers associated withthe different layers are implemented in different RAN nodes (e.g.,different eNBs), the systems and methods described herein may beapplicable to an arrangement where multiple schedulers implemented in asingle RAN node.

FIG. 2A is a system diagram illustrating an example network architecturethat may provide a WTRU multiple layers for transmission/reception. Forexample, MeNB 202 may provide a WTRU with a first layer of wirelesscoverage (e.g., a macro layer). SCeNB 204 and/or SCeNB 206 may providethe WTRU with additional layers of wireless coverage (e.g., a secondlayer, a third layer, etc.). SCeNB 204 and/or SCeNB may be provide oneor more layers of “small cells” coverage for the WTRU. One or moreSCeNBs may be logically grouped to form clusters of SCeNBs. This may bereferred to as a cluster. For example, SCeNB 204 and SCeNB 206 may beincluded in a cluster.

MeNB 202 may communicate with one or more of SCeNB 204 and/or SCeNB 206via a logical communication interface, which may be referred to as anX2bis interface. MeNB 202 may communicate with a cluster of one or moreSCeNBs using an X2bis interface. SCeNBs within a cluster arrangement maycommunicate with other SCeNBs within the cluster and/or may communicatewith a central controller (e.g., a cluster controller, a Small CellGateway (SCGW), etc.). For example, a SCGW may terminate S1-U forbearers associated with the corresponding small cell layer. The X2bisinterface may be an extension of the X2 interface (e.g., an interfaceused by an eNB to communicate with other eNBs), may be the same as theX2 interface, and/or the X2bis may be a separate logical interface(e.g., in addition to the X2 interface). The X2bis interface may be awired interface and/or may be a wireless interface. In an example, theX2bis interface may be implemented over a relatively high latencycommunication medium (e.g., and/or a communication medium over whichrelatively low latency cannot be guaranteed), for example makingcoordinated scheduling between a MeNB and an SCeNB practically difficultto implement.

FIG. 2B is a system diagram illustrating another example networkarchitecture that may provide a WTRU multiple layers fortransmission/reception. As illustrated in FIG. 2B, a MeNB maycommunicate with another MeNB via the X2′ interface and with a SCeNB viathe X2bis interface. The X2′ interface may be an extension of the X2interface, may be the same as the X2 interface, and/or may be a separatelogical interface (e.g., in addition to the X2 interface).

With multi-scheduling, a WTRU may establish a connection such that datamay be exchanged using one or more data paths, where each path may use aradio interface (e.g., Uu) associated with different network nodes(e.g., a MeNB or a SCeNodeB). The air interfaces for the different datapaths may be independently scheduled by the respective network nodes(e.g., a MeNB or a SCeNodeB).

A first RRC connection may be established between the WTRU and a MeNB.The first RRC connection may establish signaling radio bearers SRB0,SRB1 and SRB2. For example, this connection may be established accordingto LTE Release 11 principles. During RRC connection establishment of thefirst RRC connection, the WTRU may indicate a whether or not the WTRUsupports operation according to multi-scheduler principles. For example,the WTRU may indicate whether it supports multi-schedule/multi-layeroperation when indicating the WTRU operating class and/or when otherwiseindicating WTRU capabilities.

When a WTRU operates according to multi-scheduler principles, thecontrol plane may be extended in order to support multi-layer operation.For example, the control plane associated with a WTRU operatingutilizing multiple layers may be implemented using a centralized controlplane/entity, a coordinated control plane/entities, and/or a distributedcontrol plane/entity.

For example, from the perspective of the network, a centralized controlplane/entity may be characterized by a single terminating RRC instance(e.g., MeNB, another network node/entity, etc.) that is supplemented bya control function between the terminating node within the network andthe SCeNB. In an example, when utilizing a centralized control plane, acontrol function may be established between the terminating node of theRRC instance and the MeNB, for example, if the terminating instance ofthe RRC connection is logically separate from the MeNB. From theperspective of the WTRU, a centralized control plane/entity may becharacterized by a single RRC entity. The WTRU may also implement one ormore extensions to control multi-scheduler aspects (e.g., one or moreSRBs) specific to a subset of the configured serving cells/layers (e.g.,those corresponding to a SCeNB).

From the perspective of the network, a coordinated controlplane/entities may be characterized by a plurality of terminating RRCinstances (e.g., a first terminating instance in a first network nodesuch as a MeNB, a second terminating instance in a second network nodesuch as an SCeNB) that may be supplemented by a control functionimplemented between the corresponding terminating nodes. Each of the RRCinstances may implement a corresponding set of SRBs and/or acorresponding set of control functions (e.g., connection establishment,mobility control and RRM, connection release, etc.). From theperspective of the WTRU, a coordinated control plane/entities may becharacterized by a plurality of RRC entities entity. The WTRU may alsoimplement one or more extensions to the control multi-scheduler aspects(e.g., signaling received via a first RRC instance) that may trigger theestablishment of a second RRC instance. Mobility control may beperformed on a per layer basis. As an example, mobility may be performedon a per layer basis if a cluster of SCeNBs are utilized. Mobilitycontrol on a per layer basis may include each RRC instance beingindependently configurable from each other.

From the perspective of the network, distributed control plane/entitiesmay be characterized by a plurality of terminating RRC instances (e.g.,a first terminating instance in a first network node such as a MeNB, asecond terminating instance in a second network node such as an SCeNB)that may be supplemented by a control function between the terminatingnodes (e.g., between the MeNB and the SCeNB). Each RRC instance mayimplement a different set of functions (e.g., the MeNB may supportconnection establishment, RLM mobility control, NAS transport, etc.,while a SCeNB may lack support for one or more of those functions). SomeRRC functions (e.g., management of radio resources for the applicableserving cells, for example using the RRC Connection Reconfiguration) maybe supported by each of the RRC instances. Mobility control may beperformed per layer, for example, in case of a deployment with a clusterof SCeNBs, in which case mobility control may be supported by one ormore RRC instances. From the perspective of the WTRU, a distributedcontrol plane/entity may be characterized by a single RRC entity. TheWTRU may also implement one or more extensions specific to the controlof the multi-scheduler aspects. For example, one or more SRBs may bespecific to a subset of the configured serving cells/layers (e.g., SRB0,SRB1 and SRB2 may be specific to the control of the serving cells/layercorresponding to a MeNB, while SRB3 may be specific to servingcells/layer corresponding to a SCeNB). Some functions may beSRB-specific (e.g., reconfiguration of radio resources and/or mobilitymanagement), which may be applied per layer.

FIG. 3 illustrates an example implementation of a centralized controlplane. For example, the centralized control plane may include a singleterminating RRC instance at the network side (e.g., at Radio CloudNetwork Controller (RCNC) 302), a single RRC instance at WTRU 304, anduse of X2bis control. For example, WTRU 304 may establish a single RRCconnection to the network. The RRC connection may be controlled by acentralized network controller such as RCNC 302.

Within the network, the centralized network controller at which the RRCinstance is terminated may be a separate logical network node (e.g.,RCNC 302) and/or may be implemented within a RAN node (e.g., an eNB).For example, the centralized network controller may be implemented inMeNB 306 and/or SCeNB 308. RCNC 302 may be communicate via the X2bisinterface (e.g., and/or some other interface) in order to configureSCeNB 308. For example, RCNC 302 may configure one or more securityparameters, evolved packet core (EPS) bearers, radio resource management(RRM) functions, etc. for SCeNB 308 via the X2bis interface. RCNC 302may send and/or configuration parameters for SCeNB 308 (e.g., WTRUconfiguration information for one or more of PHY, MAC, RLC, PDCP, RRC,etc. for one or more serving cells of the SCeNB) via the X2bisinterface. At WTRU 304, a single RRC instance and a single RRCconnection may be used to implement the centralized control plane.

When utilizing a centralized control plane, information associated withone or more SRBs may be exchanged via multiple layers/data paths. Forexample, some data associated with an SRB may be exchanged via thelayer/data path including MeNB 306 and other data associated with theSRB may be exchanged via the layer/data path including SCeNB 308. Asshown in FIG. 3, an RRC PDU corresponding to SRB(x) may be exchangedover a data path that corresponds to a radio bearer (and/or logicalchannel (LCH)) of the MeNB and/or to a radio bearer (and/or LCH) of aSCeNB. The RRC PDU corresponding to SRB(x) may be included in atransport block associated with a first MAC instance associated with themacro layer and/or a second MAC instance associated with the small celllayer. A centralized control plane may be implemented irrespective ofhow the layer 2 protocol is split between the RCNC and the MeNB/SCeNB.

In an example, a centralized control plane may be implemented where eachSRB is associated with a given data path/layer. For example, FIG. 4illustrates an example implementation of a centralized control planewhere SRBs are associated with a single data path/layer. As shown inFIG. 4, WTRU 404 may be configured to communicate RRC PDUs associatedwith a first SRB (e.g., SRB(0, 1, 2, or x)) to RCNC 402 via a first datapath/layer that is associated with a radio bearer (and/or LCH) of MeNB406 and RRC PDUs associated with a second SRB (e.g., SRB(y)) to RCNC 402via a second data path/layer that is associated with a radio bearer(and/or LCH) of SCeNB 408. The RRC PDUs may be mapped to a transportblock associated with the appropriate LCH (e.g., a LCH of the MACinstance associated with the SRB). A centralized control plane here eachSRB is associated with a given data path/layer may be implementedirrespective of how the layer 2 protocol is split between the RCNC andthe MeNB/SCeNB.

As may be appreciated, examples may include a implementations where someSRBs, for example SRB0, SRB1, and SRB2, may be mapped to a single datapath (e.g., the data path associated with the MeNB), while other SRB(s)may be mapped to both data paths. In another example, all SRBs may besent via a single layer. For example, there may no SRBs associated withthe data path/layer for the SCeNB.

In an example, the RCNC may be co-located with and/or implemented by aMeNB. FIG. 5 illustrates an example control plane protocol stack forSRBs exchanged via the data path including a MeNB when an RRC instanceis terminated at the MeNB on the network side. If the RCNC is co-locatedwith and/or implemented by the MeNB, one or more of SRB0, SRB1, SRB2,and/or SRB3 may be exchanged via the data path including the MeNB. Forexample, a WTRU may establish an RRC connection with a MeNB, forexample, according to LTE Release 11 procedures. The MeNB may receivethe capability information for the WTRU from the WTRU that indicatedthat the WTRU supports multi-scheduler/multi-layer operation. The MeNBmay configure the WTRU to perform measurements for frequencies thatcorrespond to the Small Cell layer (e.g., intra-band measurements,inter-band measurements, etc.). The MeNB may receive a measurementreport from the WTRU, and may determine what serving cell of an SCeNBmay be suitable for offloading traffic to/from the WTRU. The MeNB mayestablish a data path for the WTRU including the SCeNB. The MeNB mayestablish a connection to the selected SCeNB in order to provide WTRUcontext information to the SCeNB. For example, the MeNB may configurethe SCeNB with parameters for setting up one or more EPS bearers such asQoS/QCI information for the WTRU, security parameters for encryptionand/or authentication, and/or the like. The MeNB may receive a responsemessage from the SCeNB that may include the Access Stratum configuration(AS-configuration) information for one or more serving cells of theSCeNB.

The MeNB may transmit a RRC connection reconfiguration message to theWTRU that may include one or more AS-configuration parameters receivedfrom the SCeNB to configured the WTRU for access to one or moreapplicable cell(s) of the SCeNB. The MeNB may receive a response fromthe WTRU indicating that it has received the configuration and/orsuccessfully connected to the SCeNB. The MeNB may receive a confirmationfrom the SCeNB that indicates that the WTRU has successfully accessedone or more serving cell of the SCeNB. The WTRU may access the SCeNBusing a random access and/or may exchange of one or more RRC messageover an SRB that was established for exchanging control data via thedata path including the SCeNB (e.g., SRB3). In an example, SRB3 may bean SRB that is established and/or dedicated to controlling the radiolink between the WTRU and the SCeNB (e.g., and/or a RAN node associatedwith a secondary data path).

FIG. 6 illustrates an example control plane protocol stack for SRBsexchanged via the data path including an SCeNB when an RRC instance isterminated at the MeNB on the network side. As shown in FIG. 6, one ormore SRBs (e.g., SRB(x) which may be SRB3) may be exchanged over thepath that includes the SCeNB. The protocol stack for such a controlplane may include the PHY, MAC, and/or RLC layers being terminated inthe SCeNB and the PDCP and/or RRC layers being terminated in the MeNB.

In order to establish dual layer connectivity, the WTRU may firstestablish an RRC connection with the MeNB, for example according to LTERelease 11 procedures. When establishing the RRC connection, the WTRUmay indicate that it supports multi-scheduler/multi-layer operation, forexample as part of the WTRU capability information. The WTRU may receivemeasurement configuration information from the MeNB. The measurementconfiguration information may include measurement information forfrequencies that corresponds to the small cell layer (e.g., intra-bandmeasurements, inter-band measurements, etc.). The WTRU may reportmeasurements according to the configured triggering criteria. The WTRUmay receive a RRC connection reconfiguration message from the MeNB, andthe RRC connection reconfiguration information may includeAS-configuration parameters for accessing one or more serving cells of aSCeNB. The WTRU may reconfigure at least a portion of its radio foroperation on the indicated carrier frequency for the SCeNB. The WTRU mayattempt to perform an initial access procedure to a serving cell of theSCeNB (e.g., receive a system information broadcast from the SCeNB). TheWTRU may send an RRC message (e.g., RRC connection reconfigurationrequest) that indicates a request to establish a SRB3 (e.g., using thesame security context as for other SRBs), which may be exchanged via thedata path including the SCeNB. The WTRU may receive a response via SRB3and/or a RRC connection reconfiguration message exchanged via SRB3(e.g., over the data path including the SCeNB) that configures one ormore cells corresponding to the SRB3 connection. The WTRU may performthe reconfiguration and transmit a RRC connection reconfigurationcomplete response message.

In an example, SRB0, SRB1, and/or SRB2 may terminate in the RCNC/MeNBand in the WTRU and may be exchanged via the data path including theMeNB. For example, SRB0, SRB1, and/or SRB2 may be associated with thecontrol plane protocol stack arrangement illustrated in FIG. 5. In anexample, SRB3 (and/or other supplemental SRBs) may terminate in theRCNC/MeNB and in the WTRU and may be exchanged via the data pathincluding the SCeNB. For example, SRB3 may be associated with thecontrol plane protocol stack arrangement illustrated in FIG. 6. SRB3 maybe used for reconfiguration (e.g., release) of radio resources and/orfor mobility management for the small cell layer.

A coordinated control plane may be characterized by a plurality ofterminating RRC instances within the network, one or more SRB sets,and/or X2bis exchange of control data. For example, a WTRU may establisha plurality of RRC connections to the network. The RRC connections maybe arranged in a hierarchical manner.

For example, from the perspective of the network both the MeNB and theSCeNB(s) may be associated with a respective RRC entity. The MeNB mayuse the X2bis interface (and/or some other interface) to configure theSCeNB with various parameters associated with the WTRU (e.g., withsecurity information, EPS bearer information, QoS information, RRMinformation, etc.). The MeNB may instruct the WTRU to establish asecondary RRC connection to a serving cell of a SCeNB. The SCeNB mayestablish the secondary RRC connection with the WTRU and may transmit aRRC connection reconfiguration message to the WTRU. The RRC connectionreconfiguration message may include AS-configuration for the applicablecell(s) of the SCeNB (e.g., WTRU configuration information for one ormore of PHY, MAC, RLC, PDCP, RRC, etc. for one or more serving cells ofthe SCeNB).

From the perspective of the WTRU, once the WTRU has established an RRCconnection with the MeNB, the WTRU may receive control signaling fromthe network that indicates that the WTRU may establish a secondary RRCconnection to a SCeNB. Such control signaling may be received in adedicated manner using the established RRC connection with the MeNB. Inan example, a paging message broadcast within a cell of a SCeNB mayindicate to the WTRU that it may establish a secondary RRC connection toa SCeNB. The page may be sent from a cluster (or a group) of SCeNBs.Prior to attempting to receive the page indicating that the WTRU mayperform multi-layer operation using a cell of the SCeNB, the WTRU mayreceive dedicated RRC signaling from the MeNB that configures asecondary RRC instance at the WTRU to perform IDLE mode mobilityprocedures for one or more cells of a given frequency band (e.g.,corresponding to the frequency band utilized by the SCeNB). The RRCconnection establishment procedure for a secondary RRC instance mayinclude an indication that the connection being established is for asecondary connection.

FIG. 7 illustrates an example control plane protocol stack for acoordinated control plane where a first RRC instance is terminated atthe MeNB and a second RRC instance is terminated at the SCeNB. As shownin FIG. 7, the data path for the first RRC connection (e.g., theconnection with the MeNB) may include a radio bearer (and/or LCH) mappedto the MeNB. For example, SRB0, SRB1, and/or SRB2 may be established viathe first RRC connection that is associated with the data path includingthe MeNB. The data path for the second RRC connection (e.g., theconnection with the SCeNB) may include a radio bearer (and/or LCH)mapped to the SCeNB. For example, instances SRB0, SRB1, and/or SRB2associated with the second RRC connection (e.g., indicated as SC-SRB0,1, 2 in FIG. 7) may be established via the second RRC connection that isassociated with the data path including the SCeNB.

A primary connection (e.g., the connection established with the MeNB)may be augmented to include an additional SRB (e.g., illustrated asSRB(x) in FIG. 7), which may be a bearer that is used to control someaspects of the secondary RRC connection (e.g., the connection associatedwith the SCeNB). For example, the additional SRB may be used to triggera connection establishment procedure and/or a release procedure over thesecondary data path/layer. RRC PDUs corresponding to the supplementalbearer may be exchanged over a data path that corresponds to a radiobearer (and/or LCH) of the MeNB.

A secondary connection (e.g., the connection established with the SCeNB)may be augmented to include an additional SRB (e.g., SRB(y), althoughnot shown in FIG. 7), which may be a bearer that is used transmit dataassociated with the primary RRC connection (e.g., the connectionassociated with the MeNB). For example, a supplemental SRB(y) (and/or asimilar implementation for multiplexing of RRC PDUs) may terminate atthe SCeNB and may be an SRB that is used to re-direct and/or forward RRCPDUs to the primary RRC instance at the MeNB. For example, data forSRB0, SRB1, or SRB2 of the primary RRC instance may be sent via SRB(y)to the SCeNB, which may forward the data to the MeNB, for example viathe X2bis interface.

FIG. 8 illustrates an example control plane protocol stack for SRBsexchanged via the data path including a MeNB when an RRC instance isterminated at the MeNB on the network side. In an example of coordinatecontrol plan operation, the MeNB may establish a primary RRC connectionwith the WTRU, for example according to LTE Release 11 procedures. TheMeNB may receive the capability information for the WTRU from the WTRUthat indicated that the WTRU supports multi-scheduler/multi-layeroperation. The MeNB may configure the WTRU to perform measurements forfrequencies that correspond to the Small Cell layer (e.g., intra-bandmeasurements, inter-band measurements, etc.). The MeNB may receive ameasurement report from the WTRU, and may determine what serving cell ofan SCeNB may be suitable for offloading traffic to/from the WTRU.

FIG. 9 illustrates an example control plane protocol stack for SRBsexchanged via the data path including a SCeNB when an RRC instance isterminated at the SCeNB on the network side. The WTRU and/or the MeNBmay trigger the WTRU to establish a secondary RRC connection, forexample a secondary connection that is terminated at the SCeNB. As anexample, the MeNB may use the primary RRC connection to instruct theWTRU to establish a secondary RRC connection with the SCeNB. In anexample, the MeNB may initiate the establishment of a connection with aSCeNB before the WTRU establishes a secondary RRC connection with theconcerned SCeNB. For example, the MeNB may establish a data path and acontrol connection to the selected SCeNB in order to transfer the WTRUcontext (e.g., via the X2bis). The MeNB may configure the SCeNB withparameters for setting up one or more EPS bearers such as QoS/QCIinformation for the WTRU, security parameters for encryption and/orauthentication, and/or the like. The MeNB may receive a response messagefrom the SCeNB that may include the AS-configuration information for oneor more serving cells of the SCeNB (e.g., system information parameters,handover command parameters similar to those of the RRC ConnectionReconfiguration with MobilityControl Information Element). The MeNB maytransmit a RRC connection reconfiguration message to the WTRU that mayinclude the AS-configuration information received from the SCeNB for theconfiguration of the applicable cell(s) of the SCeNB (e.g., theMobilityControl Information Element).

In an example, the WTRU may establish a secondary RRC connection to theSCeNB, and then the SCeNB may initiate the establishment of a connectionto the MeNB (e.g., after the establishment of the secondary RRCconnection). For example, after establishing the secondary RRCconnection with the WTRU, the SCeNB may request the establishment of adata path and a control connection to the associated MeNB in order toreceive WTRU context information from the MeNB. The request for the WTRUcontext may be sent by the SCeNB while the secondary connection is beingestablished by the WTRU (e.g., after/based on receiving the RRCconnection request sent from the WTRU. For example, the MeNB mayconfigure the SCeNB with parameters for setting up one or more EPSbearers such as QoS/QCI information for the WTRU. The MeNB and the SCeNBmay utilize different security configuration for the same WTRU. The MeNBmay receive a response message from the SCeNB indicating that the WTRUcontext information was received and/or that the secondary RRCconnection was successfully established. The MeNB may receive aconnection complete response from the WTRU and/or a confirmation fromthe SCeNB that may indicate that the WTRU has established the secondaryconnection to the SCeNB.

In an example of operation using a coordinated control plan, the WTRUmay establish a RRC connection with the MeNB (e.g., according to LTERelease 11 procedures). When establishing the RRC connection, the WTRUmay indicate that it supports multi-scheduler/multi-layer operation, forexample as part of the WTRU capability information. The WTRU may receivemeasurement configuration information from the MeNB. The measurementconfiguration information may include measurement information forfrequencies that corresponds to the small cell layer (e.g., intra-bandmeasurements, inter-band measurements, etc.). The WTRU may reportmeasurements according to the configured triggering criteria. The WTRUmay receive a RRC connection reconfiguration message from the MeNB, andthe RRC connection reconfiguration information may includeAS-configuration parameters for accessing one or more serving cells of aSCeNB. The WTRU may reconfigure at least a portion of its radio foroperation on the indicated carrier frequency for the SCeNB. The WTRU mayattempt to perform an initial access procedure to a serving cell of theSCeNB (e.g., receive a system information broadcast from the SCeNB). TheWTRU may establish a RRC connection with the SCeNB, for exampleaccording to LTE Release 11 procedures. The WTRU may transmit an RRCreconfiguration complete response to one or more of MeNB and/or theSCeNB upon successfully establishing the secondary RRC connection.

When a coordinated control plan is utilized, one or more independentSRBs may terminate at each of the RAN nodes (e.g., the MeNB and theSCeNB). For the primary RRC connection, a first set of SRBs (e.g.,including a first instance of SRB0, a first instance of SRB1, and/or afirst instance of SRB2) may terminate in the MeNB. For the secondary RRCconnection, a first set of SRBs (e.g., including a first instance ofSRB0, a first instance of SRB1, and/or a first instance of SRB2) mayterminate in the SCeNB.

A distributed control plane may be characterized by a single terminatingRRC instance at the network side, a single set of SRB0, SRB 1, and/orSRB 2, X2bis control between nodes of different layers, and the use ofan SRB (e.g., SRB3) for exchanging control data between layers.

For example, when utilizing a distributed control plane the WTRU mayestablish a single RRC connection to the network via the MeNB. Althoughthe RRC connection is established with the MeNB (e.g., the macro layer),some RRC functionality related to management of the radio resources ofserving cells corresponding to the SCeNB may be performed or implementedby the SCeNB. If the SCeNB is a member of a cluster of SCeNBs, then theSCeNB may perform some mobility-related functions. For example, if theSCeNB implements one or more RRC functions and/or RRM functions for theserving cell(s) associated with the SCeNB (e.g., a subset of the RRCfunctions and/or RRM functions), the RRC connection established betweenthe WTRU and the network may include one or more SRBs utilized tocontrol the data path between the SCeNB and the WTRU (e.g., SRB3).

At the network side, the MeNB may have a RRC entity which may be atermination point of the RRC connection. For example, SRB0, SRB1 andSRB2 may terminate in the WTRU and in the MeNB. The MeNB may use theX2bis interface (or similar) to configure the SCeNB for communicationswith the WTRU (e.g., security information, EPS bearer setup information,QoS/QCI information, etc.). The MeNB may instruct a WTRU to access aserving cell of a SCeNB. The SCeNB may establish one or moresupplemental SRB(s) (e.g., SRB3), for example for performing RRMfunctions of the serving cells associated with the SCeNB. Such asupplemental SRB may be used to facilitate some mobility-relatedfunctions in the SCeNB. The supplemental SRBs (e.g., SRB3) may terminatein the WTRU and in the SCeNB, for example even when the RRC connectionis terminated at the MeNB and not the SCeNB. The supplemental SRB may beused for control signaling that reconfigures one or more serving cellscorresponding to the SCeNB (e.g., WTRU configuration information for oneor more of PHY, MAC, RLC, PDCP, etc. for one or more serving cells ofthe SCeNB).

From the perspective of the WTRU, once the WTRU has established an RRCconnection with the MeNB, the WTRU may receive control signaling fromthe network that indicates that the WTRU may establish a secondary RRCconnection to a SCeNB. Such control signaling may be received in adedicated manner using the established RRC connection with the MeNB. Inan example, a paging message broadcast within a cell of a SCeNB mayindicate to the WTRU that it may establish a secondary RRC connection toa SCeNB. The page may be sent from a cluster (or a group) of SCeNBs.Prior to attempting to receive the page indicating that the WTRU mayperform multi-layer operation using a cell of the SCeNB, the WTRU mayreceive dedicated signaling from the MeNB that configures the WTRU tomonitor the paging channel of a suitable cell of the SCeNB a givenfrequency band. The WTRU may accesses a cell of a SCeNB using a randomaccess procedure. The random access may be a dedicated random access,for using RACH parameters (e.g., a dedicated RACH preamble) received inthe dedicated control signaling sent from the MeNB. The WTRU may receiveRRC signaling that reconfigures the serving cells corresponding to theSCeNB, for example via SRB3.

FIG. 10 illustrates an example control plane protocol stack for adistributed control plane where the RRC instance is terminated at theMeNB. As shown in FIG. 10, an RRC PDU corresponding to a transmissionfor a given SRB of the RRC connection may be exchanged over a data paththat corresponds to a radio bearer (and/or LCH) of the MeNB and/or to aradio bearer (and/or LCH) of the SCeNB. For example, RRC PDUscorresponding to a transmission for SRBs 0, 1, and 2 may be exchangedover a data path that corresponds to a radio bearer (and/or LCH) of theMeNB. This may be represented as SRB0, 1, 2 in FIG. 10. RRC PDUscorresponding to a transmission for a supplemental SRB (e.g., SRB3) maybe exchanged over a data path that corresponds to a radio bearer (and/orLCH) of the SCeNB. This may be represented as SRB(x) FIG. 10. The SCeNBmay forward control data associated with SRB3 to the MeNB via the X2bisinterface. Thus, in an example for the distributed control planearchitecture, some RRC related functionality may be implemented by theSCeNB (e.g., related to SRB3) even though no RRC connection and/or noSRBs are terminated in the small cell layer. Such a subset of RRCfunctionality is illustrated by the SCeNB including the SC-RRC layer ofthe protocol stack in FIG. 10 (e.g., representing limited RRCfunctionality that is implemented at the small cell).

In an example of network side functionality in the case of a distributedcontrol plane, the MeNB may establish a RRC connection with the WTRU,for example, according to LTE R11 procedures. An example of such may beshown in FIG. 11. FIG. 11 is a diagram illustrating an example of acontrol plan protocol stack comprising a distributed approach for SRB0,SRB1, and SRB2 of MeNB RRC. The MeNB may receive the WTRU's capabilitiesfor support for multi-scheduler operation as part of the connectionestablishment procedure. The MeNB may configure the WTRU withmeasurements for frequencies that correspond to the Small Cellenhancement layer (e.g., intra-band or inter-band measurements). TheMeNB may receive a measurement report from the WTRU, and may determinewhat serving cell of a SCeNB may be suitable for offloading trafficto/from the WTRU. The MeNB may establish a data path and a controlconnection to the selected SCeNB for the WTRU's context. The MeNB mayconfigure the SCeNB with, for example, parameters for setting up one ormore EPS bearers with QoS/QCI information for the WTRU as well as withsecurity parameters for encryption and authentication. The MeNB mayreceive from the SCeNB a response message that may includeAS-configuration for at least one serving cell of the SCeNB. The MeNBmay transmit a RRC connection reconfiguration message to the WTRU thatmay include the configuration parameters received from the SCeNB for theconfiguration of the applicable cell(s) of the SCeNB. The MeNB mayreceive a complete response from the WTRU or a confirmation from theSCeNB, which response may indicate that the WTRU has accessed at leastone serving cell of the SCeNB (e.g., a successful random access and/orexchange of at least one RRC message over SRB3). SRB3 may terminate inthe SCeNB. For example, this may be shown in FIG. 12. FIG. 12 is adiagram illustrating an example of a control plane protocol stackcomprising a distributed approach for SRB 3 of SCeNB.

In an implementation, the WTRU may establish a RRC connection with theMeNB, for example, according to LTE R11 procedures. For example, thismay be shown in FIG. 11. The WTRU may include whether or not it supportsmulti-scheduler operation in its WTRU capabilities. The WTRU may receivefrom the MeNB a measurement configuration including measurements forfrequencies that corresponds to the Small Cell enhancement layer (e.g.,intra-band or inter-band measurements). The WTRU may report measurementsaccording to the configured triggering criterion. The WTRU may receive aRRC connection reconfiguration message from the MeNB with theAS-configuration parameters to access one or more serving cell of aSCeNB. The WTRU may reconfigure at least part of its radio for operationon the selected carrier frequency and perform an initial access to theserving cell (e.g., reception of system broadcast). The WTRU may includean initial RRC message such as, but not limited to a request toestablish a SRB3 that terminates in the SCeNB. This may be done usingthe same security context as for other SRBs. For example, this may beshown in FIG. 12. The WTRU may receive a response on SRB3 and/or a RRCconnection reconfiguration message on SRB3 that configures one or morecells corresponding to the SRB3 connection. The WTRU may perform thereconfiguration and transmit a complete response over SRB3 as a responseto the configuration request from the SCeNB. The WTRU may transmit acomplete response to the MeNB over SRB1 or SRB2 in response to therequest to access the SCeNB.

SRB3 may terminate in the WTRU and in a SCeNB. A supplemental SRB may beused once security is started. SRB3 may be used for RRM (e.g.,configuration, reconfiguration) of the serving cell(s) associated with aSCeNB, and/or for mobility control in the Small Cell enhancement layer.

When multiple schedulers are utilized for transmitting over multipledata paths, the mapping between DRBs/SRBs and the multiple data pathsmay vary depending on the how the protocol stack for transmitting thedata is split between different network nodes. For example, a first datapath may be established from the WTRU to the network via a MeNB (e.g., amacro layer) and additional data path(s) may be established from theWTRU to the network via one or more SCeNBs. One or more protocol stacksmay be defined for the user plane and/or for the control plane in orderto support multi-layer (e.g., multi-scheduler) transmission.

For example, the X2bis interface and/or some other interface between theMeNB and SCeNB may be used to implement various protocol stackarrangements in support of multi scheduler operation. For a given WTRU,the data path for the user plane and the data path for the control planemay be realized, at least in part, based on communications exchanged viathe X2bis interface.

For example, multiple data paths for a given WTRU may be establishedsuch that the data paths are split within the network above the PDCPlayer. Such an architecture may result in each of the MeNB and the SCeNBincluding functionality corresponding to the PHY layer, the MAC layer,the RLC layer, and the PDCP layer. The control plane may be implementedsuch that a PDCP entity associated with a given radio bearer (e.g., DRBand/or SRB) may be located in the network entity that transmits and/orreceives control data. For example, the PDCP entity used to transmitcontrol data via the SCeNB may be located in the SCeNB and the PDCPentity used to transmit data via the MeNB may be located in the MeNB. Inan example, user plane data and/or control plane data may be carriedover a radio bearer that may be mapped to a single data path (e.g., to aDRB/SRB with a single SAP). In another example, user plane data and/orcontrol plane data may be carried over a radio bearer that may be mappedto a plurality of data paths (e.g., to a DRB/SRB with multiple SAPs).Each PDCP entity (e.g., the PDCP entity of the SCeNB, the PDCP entity ofthe MeNB) may include a security state machine for its respective datapath.

In an example, multiple data paths that are split above the PDCP layerin the network may be implemented using one or more radio bearers thatare associated with a single SAP at the network (e.g., the MeNB or theSCeNB). To support multi-scheduler operation, one or more DRBs and/orSRBs may be transferred between the data paths (e.g., DRB/SRB mobility).For example, an SRB associated with the MeNB may be offloaded to aSCeNB. If a distributed control plane is utilized (e.g., there may besome RRC functionality at both the MeNB and the SCeNB), then SRB3 orsome other SRB may be used to exchange mobility related controlinformation.

For example, if a given radio bearer is associated with a single SAP inthe network, for the user plane an EPS radio access bearer (RAB) may beimplemented using a single DRB SAP. For example, FIG. 13 illustrates anexample protocol stack that may be used for user plane data paths (e.g.,the WTRU-MeNB data path and the WTRU-SCeNB data path) when the datapaths are split above the PDCP layer in the network.

In the control plane, NAS signaling and/or RRC signaling may betransmitted over a single SRB associated with a single SAP. Depending onwhether a centralized control plane, coordinated control plane, and/ordistributed control plane is utilized, the mapping of SRBs to the datapaths, the mobility of SRBs, and/or the protocol stack realization forthe control plane within the network may be varied.

For example, a centralized control plane may be implemented such that asingle SRB SAP is utilized for NAS and/or RRC signaling. For example,RRC PDUs for SRB0, SRB1, and/or SRB2 may be generated by the RCNCentity, which may be implemented in the MeNB. Additional extensionsand/or additional information elements may be exchanged via the MeNB inorder to manage the radio connection between the WTRU and the SCeNB(e.g., trigger establishment, mobility, and/or release of a secondaryRRC connection). The RRC PDUs for SRB0, SRB1, and/or SRB2 may be maytransmitted to the WTRU from a serving cell of the MeNB. In an example,RRC PDUs for SRB0, SRB1, and/or SRB2 may be exchanged via the RAN nodeto which the WTRU initially established the RRC connection (e.g., priorto initiating multi-scheduler/multi-layer operation). RRC PDUscorresponding to a SRB dedicated to the SCeNB (e.g., SRB3) may beexchanged in a serving cell of the SCeNB.

FIG. 14 illustrates an example protocol stack where SRBs may beassociated with a single SAP and the data paths are split above the PDCPlayer in the network using a centralized control plane. For example, RRCPDUs for a given SRB may be transmitted over a single data path (e.g.,SRB0, SRB1, and/or SRB2 over the data path associated with the MeNB andSRB3 over the data path associated with the SCeNB). The radio bearersfor the different data paths may be associated with different/separatePDCP entities. From the perspective of the network, the PDCP layerassociated with the connection to the WTRU may be located in the MeNBand in the SCeNB (e.g., not shown in FIG. 14) or may be located in theRCNC (e.g., as illustrated in FIG. 14). In an example, both the PDCPlayer and the RLC layer on the network side may be located at the RCNC.

In an example, a coordinated control plane may be implemented such thata single SRB SAP is utilized for NAS and/or RRC signaling. For example,when the RRC connection uses a coordinated control plane, RRC PDUs for agiven SRB (e.g., SRB0, SRB1, and/or SRB2) may be transmitted over asingle data path such as the data path associated with the MeNB. Othercontrol data designed to trigger establishment, mobility, and/or releaseof a secondary RRC connection may also be exchanged via a single datapath associated with the MeNB (e.g., via a serving cell of the MeNB). Inan example, RRC PDUs for SRB0, SRB1, and/or SRB2 may be exchanged viathe RAN node to which the WTRU initially established the RRC connection(e.g., prior to initiating multi-scheduler/multi-layer operation). For acoordinated control plane, RRC PDUs for SRB0, SRB1, and/or SRB2 may begenerated by the SCeNB, and the SCeNB may exchange the locally generatedRRC PDUs via a serving cell of the SCeNB. For example, for a given radiobearer, FIG. 8 and FIG. 9 may illustrate example where eachcorresponding radio bearer has a separate PDCP entity for each RRCinstance utilizing a coordinated control plane.

In an example, a distributed control plane may be implemented such thata single SRB SAP is utilized for NAS and/or RRC signaling. For example,when the RRC connection uses a distributed control plane, RRC PDUs forSRB0, SRB1, and/or SRB2 may be generated by the MeNB entity. Additionalextensions and/or additional information elements may be exchanged viathe MeNB in order to manage the radio connection between the WTRU andthe SCeNB (e.g., trigger establishment, mobility, and/or release of asecondary RRC connection). The RRC PDUs for SRB0, SRB1, and/or SRB2 maybe may transmitted to the WTRU from a serving cell of the MeNB. In anexample, RRC PDUs for SRB0, SRB1, and/or SRB2 may be exchanged via theRAN node to which the WTRU initially established the RRC connection(e.g., prior to initiating multi-scheduler/multi-layer operation). RRCPDUs corresponding to a SRB dedicated to the SCeNB (e.g., SRB3) may beexchanged in a serving cell of the SCeNB. For example, RRC PDUs for SRB3may be generated in the SCeNB and transferred to the WTRU via a servingcell of the SCeNB. FIG. 10 may illustrate example where eachcorresponding radio bearer has a separate PDCP entity for each RRCinstance utilizing a distributed control plane.

In an example, rather than or in addition to mapping a given radiobearer to a single SAP, a single RB may be mapped to a plurality of SAPs(e.g., over a plurality of logical channels). For example, in the userplane an EPS RAB with multiple DRB SAPs may be used. Mapping of a singleEPS RAB over a plurality of E-UTRA DRBs may be implemented using avariety of techniques, for example depending on whether the data is forthe data plane or the control plane and/or whether a centralized,coordinated, or distributed control plane is utilized. For example, datafor the user plane may be exchanged over one of a plurality of datapaths. Data corresponding to a given EPS bearer may be mapped over oneor more SAPs, where each SAP may correspond to a DRB and/or to a LCH ofa different MAC instance. FIG. 15 illustrates an example for a data pathsplit above the PDCP layer for the user plane where multiple DRB SAPsare utilized. For example, IP packets for a given EPS bearer may beexchanged over either data path (e.g., the path associated with the MeNBor the path associated with the SCeNB).

If multiple radio bearer SAPs are utilized, for the control plane NASand/or RRC signaling may be transmitted over multiple SRB SAPs. Forexample, a single SRB may be mapped over a plurality of SAPs (e.g., overa plurality of logical channels). Data corresponding to a given SRB(e.g., one of SRB0, SRB1, SRB2, and/or a supplemental SRB such as SRB3)may be mapped over one or more SAPs, where each SAP may correspond to adifferent MAC instance and be transmitted via a different RAN node(e.g., the MeNB or the SCeNB).

FIG. 16 illustrates an example protocol stack where SRBs may beassociated with multiple SAPs and the data paths are split above thePDCP layer in the network using a centralized control plane. Forexample, RRC PDUs for a given SRB may be transmitted over a multipledata path (e.g., the data path associated with the MeNB and/or the datapath associated with the SCeNB). A given radio bearer may utilize theservices of multiple PDCP entities (e.g., a PDCP entity at the SCeNB anda PDCP entity at the MeNB). From the perspective of the network, thePDCP layer associated with the connection to the WTRU may be located inthe MeNB and in the SCeNB (e.g., as shown in FIG. 16) or may be locatedin the RCNC (e.g., not shown in FIG. 16). In an example, both the PDCPlayer and the RLC layer on the network side may be located at the RCNC.For the perspective of the network, each SAP associated with a givenradio bearer may correspond to a logical channel that is managed by adifferent scheduler. The WTRU may receive control data that correspondsto a given SRB over different logical channels of different MACinstances.

In an example, a coordinated control plane may be implemented such thata radio bearer (e.g., SRB) may use the services of a plurality of PDCPentities. For example, when the RRC connection uses a coordinatedcontrol plane, RRC PDUs for a given SRB (e.g., SRB0, SRB1, and/or SRB2)may be transmitted over a multiple data paths. For example, multiplexingand/or demultiplexing of the RRC PDUs associated with a given SRB of afirst RRC entity and a RRC PDUs associated with an SRB of a second RRCentity may be performed.

In an example, a distributed control plane may be implemented such thata radio bearer (e.g., SRB) may use the services of a plurality of PDCPentities. For example, a radio bearer associated with the RRC entity inthe MeNB may use the services of a PDCP entity located in the SCeNB.FIG. 3 may illustrate an example of a distributed control plane where agiven SRB may be mapped to a plurality of radio bearer SAPs.

In an example, rather than splitting the data paths above the PDCPprotocol stack within the network, the data paths/layers utilized by theWTRU may be split above the RLC layer. Thus the PDCP layer may beincluded at a single node within the network, and the PDCP layer PDUs tobe transmitted to the WTRU may be mapped to a plurality of RLC SAPs(e.g., over a plurality of logical channels). The PDCP layer may includethe functionality of a plurality of PDCP entities. For example, a PDCPentity may be associated with a specific DRB and/or SRB that has beenallocated to the WTRU. Thus, if the WTRU has been allocated a pluralityof DRBs, there may be a plurality of PDCP entities (e.g., both withinthe WTRU and within the network) that processes PDCP packets (e.g., SDUsand PDUs) corresponding to the DRB/SRB associated with the specificentity.

If multiple RLC instances are utilized within the network (e.g., a firstRLC instance at the MeNB, and a second RLC instance at the SCeNB), thenthe packets to/from a given PDCP entity may be mapped to one or more ofthe RLC instances at the different transmission sites in a variety ofways. For example, the data associated with a given PDCP entity (e.g.,user plane data associated with a given DRB) may be mapped such that thePDCP entity may transfer associated PDCP PDUs over a single RLC SAP(e.g., using a direct mapping between a PDCP entity and an RLC entity ata given RLC instance). In another example, a PDCP entity (e.g., whichmay correspond to a given DRB) may be configured to transfer associatedPDCP PDUs using one or more of a plurality of RLC SAPs, for example,where data from the PDCP entity may be transferred using a first RLCinstance (e.g., at the MeNB) at some times and transferred using asecond RLC instance (e.g., at the SCeNB) at other times. The PDCP entityused to transfer data within the network may or may not be co-located inthe same node as the RLC entity utilized to transmit the data.

For example, in the user plane PDCP entities (e.g., in the network, inthe WTRU, etc.) may be configured to transmit and/or receive data usingmultiple RLC SAPs. Utilization of multiple RLC SAPs may result in datafor a given DRB being exchanged over multiple data paths, where the datapaths diverge below the PDCP layer in the network. PDCP PDUscorresponding to a given EPS bearer may be mapped over one or more RLCSAPs, where each SAP may correspond to a LCH of a different MACinstance. For example, FIG. 17 and FIG. 18 illustrate example protocolstacks that may be utilized for transferring user plane data when thedata paths are split below the PDCP layer in the network.

A PDCP entity may utilize a plurality of data paths (e.g., associatedwith different RLC instances located at different network entities) fortransferring control data (e.g., data of one or more SRBs). For example,the data associated with a given PDCP entity (e.g., control plane dataassociated with a given SRB) may be mapped such that the PDCP entity maytransfer associated PDCP PDUs over a single RLC SAP (e.g., using adirect mapping between a PDCP entity and an RLC entity at a given RLCinstance). In another example, a PDCP entity (e.g., which may correspondto a given SRB) may be configured to transfer associated PDCP PDUs usingone or more of a plurality of RLC SAPs, for example, where data from thePDCP entity may be transferred using a first RLC instance (e.g., at theMeNB) at some times and transferred using a second RLC instance (e.g.,at the SCeNB) at other times. For example, PDCP PDUs associated with agiven SRB (e.g., one of SRB0, SRB1, SRB2 or a supplemental SRB) may bemapped over one or more RLC SAPs.

FIG. 19 illustrates an example control plane protocol stack of a datapath split above RLC where PDCP PDUs may be transferred over a pluralityof data paths. For example, as shown in FIG. 19, PDCP PDUs associatedwith SRB(x) may be transferred via the data path associated with theMeNB (e.g., using an RLC entity located at the MeNB) and/or may betransferred via the data path associated with the SCeNB (e.g., using anRLC entity located at the SCeNB). In an example, such an arrangement maybe utilized to implement a centralized control plane approach asdescribed herein. The PDCP entity for a given SRB may be located at theMeNB. A first RLC entity utilized to transmit data for the PDCP entitymay be co-located with the PDCP entity in the MeNB. A second RLC entityutilized to transmit data for the PDCP entity may be located in theSCeNB. FIG. 20 illustrates an example of the data path associated withthe SCeNB when the data split occurs below the PDCP layer (e.g., abovethe RLC layer).

In an example, a coordinated control plane may be implemented such thata radio bearer (e.g., SRB) may use the services of a plurality of RLCentities. For example, when the RRC connection uses a coordinatedcontrol plane, RRC PDUs for a given SRB (e.g., SRB0, SRB1, and/or SRB2)may be transmitted over a multiple data paths. For example, multiplexingand/or demultiplexing of the RRC PDUs associated with a given SRBtransferred via a first RLC entity and a RRC PDUs associated with an SRBof a second RRC entity transferred via a second RLC entity may beperformed.

For the distributed control plane, RRC PDUs associated with a PDCPentity located in the MeNB may utilize services provide by an RLC entitylocated in the SCeNB. For example, such an architecture may use methodssimilar to those described with respect to a distributed control planewhen the data split occurs above the PDCP layer (e.g., FIG. 16).

In an example, the data path split may occur above the MAC layer (e.g.,below the RLC layer). In such an architecture, the PDCP layer and theRLC layer within the network may be implemented in the same node withinthe network (e.g., in the MeNB). However, each data path may beassociated with its own MAC instance that is associated with one of theplurality of data paths. FIG. 21 illustrates an example control planeprotocol stack that may be utilized if the data paths are split abovethe MAC layer. FIG. 22 illustrates an example user plane protocol stackthat may be utilized if the data paths are split above the MAC layer.

In order to support a multi-scheduler architecture (e.g., transmissionand/or reception via independently scheduled data paths sent viadifferent serving sites), the Layer 2 structure in the uplink and/ordownlink may be modified from the structure utilized fortransmission/reception via a single data path. For example, at the WTRUuplink data (e.g., RLC PDU, MAC SDU, etc.) from a logical channel may bemultiplexed onto transport blocks delivered to one of a set transportchannels (e.g., UL-SCH) associated with a serving site or MAC instance.FIG. 23 illustrates an example Layer 2 structure for uplink multi-siteoperation (e.g., utilizing a segregated UL). Data associated with aspecific radio bearer (e.g., PDCP PDU) may be mapped by an RLC instanceto a single logical channel. Mapping data from a radio bearer to asingle RLC instance may be referred to as a segregated UL transmissionscheme. When a segregated UL transmission scheme is utilized, a givenradio bearer may be mapped to a given logical channel that is associatedwith one of the MAC instances. Although the data may be sent to thenetwork via multiple transport channels (e.g., there may be a UL-SCHtransport channel for each component carrier of the MAC instance), datamapped to a given logical channel may be transported to the network viathe same MAC instance if a segregated UL transmission scheme isutilized. As an example, a segregated UL transmission scheme may be usedfor user plane data transfers where a single radio bearer SAP (e.g., asingle RLC SAP) is utilized with a protocol stack that is split abovethe PDCP layer, although the segregated UL transmission scheme may beused with other architectures as well.

Data from a specific radio bearer (e.g., PDCP PDU) may mapped to morethan one logical channel and/or may be mapped to a plurality ofsub-logical channels. Data from a radio bearer that is split between aplurality of logical channels may processed by different RLC instances(e.g., where each RLC instance is associated with and/or located at adifferent transmission/reception site within the network). For example,a plurality of RLC instances may be configured to segment and/orretransmit data associated with a given radio bearer. Each RLC instancemay be associated with a different logical channel or sub-logicalchannel for the radio bearer. Since separate RLC instances may beutilized for processing data associated with single radio bearer, such ascheme may be referred to as split RLC UL transmission scheme. FIG. 24illustrates an example Layer 2 structure for uplink multi-site operationwhere a split RLC transmission scheme is utilized. At the WTRU, datafrom a logical channel associated a given RLC instance may be associatedwith a specific MAC instance. Although the data may be sent to thenetwork via multiple transport channels (e.g., there may be a UL-SCHtransport channel for each component carrier of the MAC instance), datamapped to a given logical channel may be transported to the network viathe same MAC instance. As an example, a split RLC UL transmission schememay be used for transmitting user plane data where multiple SAPs areutilized with a protocol stack that is split above the RLC layer,although the split RLC UL transmission scheme may be used with otherarchitectures as well.

In an example, at the WTRU uplink data associated with a given logicalchannel may be multiplexed onto transport blocks associated withtransport channels for multiple serving sites. For example, uplink datafrom a specific logical channel may be allowed to be multiplexed ontotransport blocks delivered to a transport channel associated with any ofthe serving sites (e.g., any transmission/reception point in thenetwork). FIG. 25 illustrates an example Layer 2 structure where a datafor a given logical channel may be mapped to a plurality of transportchannels and the transport channels may be associated with differentserving sites. Mapping data from a logical channel to transport channelsassociated with different transmission/reception sites in the networkmay be referred to as a pooled UL transmission scheme. When a pooled ULtransmission scheme is used, uplink data (e.g., RLC SDUs) from a givenradio bearer may be delivered to one of a plurality of logical channelsthat are configured for the radio bearer. A plurality of MAC instancesand/or a plurality of corresponding logical channels may be configuredfor use by the bearer (e.g., specified in the bearer configuration). Asan example, a pooled UL transmission scheme may be used for user planedata transfers where any MAC PDU may be used for transporting any RLCPDU. For example, a pooled UL transmission scheme may be applied to anarchitecture where the transmission paths are split above the MAC layer,although the pooled UL transmission scheme may be utilized for otherarchitectures as well.

At the network side, MAC SDUs may be de-multiplexed from a transportblock decoded at a serving site that is associated with the UL-SCH usedfor the transmission. The MAC SDUs may be processed by an RLC entity atthe serving site and/or may be relayed to a second site (e.g., a primaryserving site) for processing by an RLC entity at the second site. Ifpooled UL is utilized, one or more serving sites may relay data (e.g.,MAC SDUs) to the serving site where the RLC entity configured to processdata associated with the concerned logical channel is located.

FIG. 26 illustrates an example of Layer 2 structure for downlinkmulti-site operation that may be used for a segregated DL transmissionscheme. At the network side, downlink data from a logical channel may bemultiplexed onto transport blocks delivered to one of a set transportchannels (e.g., DL-SCH) associated with a serving site or MAC instance.At the WTRU side, downlink data associated with a given logical channelmay be de-multiplexed from transport blocks received via one of a set oftransport channels (e.g., DL-SCH) associated with a specific servingsite or MAC instance. Mapping data from a radio bearer to a single RLCinstance may be referred to as a segregated DL transmission scheme. Whena segregated DL transmission scheme is utilized, a given radio bearermay be mapped to a given logical channel that is associated with one ofthe MAC instances. Although the data may be sent to the WTRU viamultiple transport channels (e.g., there may be a DL-SCH transportchannel for each component carrier of the MAC instance), data mapped toa given logical channel may be transported to the WTRU via the same MACinstance if a segregated DL transmission scheme is utilized.

FIG. 27 illustrates an example of Layer 2 structure for downlinkmulti-site operation that may be used for a split RLC DL transmissionscheme. Data from a specific radio bearer (e.g., PDCP PDU) may mapped tomore than one logical channel and/or may be mapped to a plurality ofsub-logical channels. Data from a radio bearer that is split between aplurality of logical channels may processed by different RLC instances(e.g., where each RLC instance is associated with and/or located at adifferent transmission/reception site within the network). For example,a plurality of RLC instances may be configured to segment and/orretransmit data associated with a given radio bearer. Each RLC instancemay be associated with a different logical channel or sub-logicalchannel for the radio bearer. Since separate RLC instances may beutilized for processing data associated with single radio bearer, such ascheme may be referred to as split RLC DL transmission scheme. At thenetwork, data from a logical channel associated with a given RLCinstance may be associated with a specific MAC instance. Although thedata may be sent to the WTRU via multiple transport channels (e.g.,there may be a DL-SCH transport channel for each component carrier ofthe MAC instance), data mapped to a given logical channel may betransported to the WTRU via the same MAC instance.

In an example, at the network downlink data associated with a givenlogical channel may be multiplexed onto transport blocks associated withtransport channels for multiple serving sites. For example, downlinkdata from a specific logical channel may be allowed to be multiplexedonto transport blocks delivered to a transport channel associated withany of the serving sites (e.g., any transmission/reception point in thenetwork). FIG. 28 illustrates an example Layer 2 structure wheredownlink data for a given logical channel may be mapped to a pluralityof transport channels and the transport channels may be associated withdifferent serving sites. Mapping downlink data from a logical channel totransport channels associated with different transmission/receptionsites in the network may be referred to as a pooled DL transmissionscheme. When a pooled DL transmission scheme is used, downlink data(e.g., RLC SDUs) from a given radio bearer may be delivered to one of aplurality of logical channels that are configured for the radio bearer.A plurality of MAC instances and/or a plurality of corresponding logicalchannels may be configured for use by the bearer (e.g., specified in thebearer configuration). As an example, a pooled DL transmission schememay be used for user plane data transfers where any MAC PDU may be usedfor transporting any RLC PDU.

If one or more bi-directional logical channels (e.g., a dedicatedcontrol channel (DCCH) and/or a bi-directional dedicated traffic channel(DTCH)) are utilized, different combinations of uplink and downlinktransmission schemes may be utilized. For example, a segregated DLtransmission scheme and pooled UL transmission scheme may be used for agiven logical channel. In an example, a serving site associated with alogical channel in the DL may be different from the serving siteassociated with the logical channel in the UL. For example, a segregatedDL transmission scheme and a segregated UL transmission scheme may beused for a given logical channel. The RLC entity at the network side maybe operating at a first serving site in the network, and the DL-SCH maybe transmitted from the first serving site. However, although there maybe no RLC entity at a second serving site, UL MAC SDUs may still betransmitted to and decoded at a second serving site. The UL MAC SDUstransmitted to the second serving site may be relayed to the first sitefor processing by the RLC entity. Such a scheme where a first servingsite includes an RLC entity (e.g., and/or the DL-SCH is transmitted fromthe first serving site) but UL MAC SDUs may still be transmitted to thesecond serving site (e.g., where the second serving site lacks an RLCentity and forwards the UL MAC SDUs to the second serving site afterdecoding) may be referred to as “decoupled UL/DL.” In an example, ssegregated DL transmission scheme and a segregated UL transmissionscheme may be used for one or more bi-directional logical channels. Forexample, the serving site corresponding to the DL transmission site forthe logical channel and the serving site corresponding to the ULreception point for a bi-directional logical channel may be the sameserving site, and an RLC entity may operate at this serving site withoutrelaying MAC SDUs to another serving site.

Higher layers (e.g., RRC) may be used to configure the uplink and/ordownlink transmissions schemes to be utilized for a given transmissionsite and/or for a given logical channel. For example, when the WTRUreceives RRC signaling configuring a given logical channel, the RRCsignaling may indicate whether a pooled transmission scheme (e.g., ULand/or DL) or a segregated transmission scheme (e.g., UL and/or DL) isto be used for the logical channel. For example, if a segregated DLtransmission scheme and/or a segregated UL transmission scheme isutilized, RRC signaling may indicate a mapping that is indicative ofwhich of one or more serving site(s) the logical channel should betransmitted to and/or received from. In an example, the mapping oflogical channels to serving sites may be predetermined for one or morelogical channels, and the WTRU may implicitly know which serving sitethe logical channel is associated with without receiving an explicitmapping. For example, logical control channels (e.g., DCCH) may bemapped to transport channels associated with a primary serving site.Logical traffic channels (e.g., DTCH) may be mapped to transportchannels associated with a secondary serving site.

If a segregated DL transmission scheme and/or a segregated ULtransmission scheme is utilized, RRC signaling may be used to configurethe mapping between the logical channel and an associated serving site.For example, the RRC signaling used to configure the logical channel foruse by the WTRU may include an indication of a logical channel identityand a serving site identity (e.g., and/or a MAC instance identity) sothat the WTRU knows which serving site should be used for the logicalchannel. In an example, rather than or in addition to using a servingsite identity (e.g., and/or MAC instance identity), the RRC signalingused to configure the logical channel may identify the mapping byincluding the logical channel identity and a serving cell identity(e.g., where the serving cell is associated with one of the servingsites). A plurality of logical channels may be configured together to beassociated with a certain serving site. For example, a logical channelgroup may be identified by a logical channel group identity and aserving site identity (e.g., and/or a serving cell identity). In anexample, WTRU may be able to implicitly determine which serving site agiven logical channel is associated with based on the logical channelidentity for that logical channel. For example, certain logical channelidentities may be associated with a primary serving site and otherlogical channel identities may be associated with a secondary servingsite.

In an example, the subset of logical channels from which data may bemultiplexed into transport blocks of one or more transport channelsassociated with a specific serving site (e.g., and/or MAC instance) maybe referred to as a “logical channel scheduling group” for the servingsite or MAC instance. From the above layer 2 structures, the UL (and/orDL) logical channel scheduling groups of different serving sites may beindependent of each other (e.g., the processing at higher layers doesnot overlap), for example, in case of a segregated UL transmissionscheme (e.g., and/or a segregated DL transmission scheme) is used.Similarly, if a split RLC UL transmission scheme (e.g., and/or a splitRLC DL transmission scheme) is utilized, the processing paths aboveLayer 2 may be independent of each other.

An example use case for the secondary serving site may be the case of DLdata transmission offload. For example, a WTRU may originally connect toa primary serving site (e.g., which may correspond to a MeNB), but mayreceive a reconfiguration from the primary serving site thatreconfigures one or more radio bearers (e.g., and/or logical channels),to be transmitted to and/or received from a secondary serving site. Asan example, one or more downlink data channels may be reconfigured to bereceived via a secondary serving site. Such a scheme may relieve theprimary serving site from having to transmit as much data to the WTRU,for example during periods where the WTRU may be well served by one ormore small cells. Since the small cells may serve fewer WTRUs than areserved in a macro cell, offloading DL data transmissions to the smallcells may save network resources while still maintaining a desired levelof service for the WTRU. In an example, the downlink data to bedelivered to the WTRU may be received by the MeNB and forwarded orrelayed to the SCeNB for delivery to the WTRU. Examples for processingthe downlink data when the downlink data may is relayed by a primaryserving site (e.g., a MeNB) to a secondary serving site (e.g., a SCeNB)for delivery to the WTRU are described herein.

How DL data to be delivered to the WTRU is processed by the networkand/or the WTRU may depend on the location of the RLC entity associatedwith the DL data within the network. For example, the RLC entityprocessing the downlink data for a radio bearer may be operating in thesecondary serving site (e.g., in the SCeNB). If the RLC entity islocated in the secondary serving site, the RLC entity within the networkmay generate RLC PDUs and segments thereof whose size may be adapted tothe transport block size applicable to the current radio conditions. Thecorresponding logical channel associated with the generated RLC PDUs maybe mapped to the DL-SCH from the secondary serving site, for exampleusing a segregated DL transmission scheme.

For bi-directional logical channels, if the RLC entity at the networkside is located at the secondary serving site, the DL transmissionsassociated with the bi-directional logical channel may be sent from thesecondary serving site and one or more options may be used by the WTRUfor transmitting UL data associated with the bi-directional logicalchannel. For example, the UL data for the bi-directional logical channelmay be mapped to a UL-SCH associated with the secondary serving site(e.g., a segregated UL transmission scheme to the secondary servingsite). If the UL data is transmitted to the secondary serving site bythe WTRU, the same RLC entity at the network side may processes bothuplink and downlink data for the bi-directional logical channel. ThePDCP entity used to process the uplink and/or downlink data for thebi-directional logical channel may also operate at the secondary servingsite.

In an example, the UL data for the bi-directional logical channel may bemapped to a UL-SCH associated with the primary serving site (e.g., asegregated UL transmission scheme to the primary serving site). Inanother example, the UL data for the bi-directional logical channel maybe mapped to a UL-SCH associated with either primary serving site and/orthe secondary serving site (e.g., pooled UL transmission scheme).

For example, UL data for the bi-directional logical channel may bemapped to a UL-SCH associated with the primary serving site, for examplewhere UL transmissions to the secondary serving site are not performedby the WTRU. However, the RLC entity at the network side may still belocated at the secondary serving site even when UL transmissions to arenot performed to the secondary serving site. If the UL data for thebi-directional logical channel is mapped to a UL-SCH associated with theprimary serving site, RLC PDUs that are de-multiplexed from uplinktransport blocks that are decoded at the primary serving site may berelayed by the primary serving site to the secondary serving site forprocessing by the RLC entity at the secondary serving site.

In an example, RLC PDUs transmitted by the WTRU that are associated witha bi-directional logical channel whose DL data is transmitted via thesecondary serving site may be de-multiplexed from uplink transportblocks that may be received by and decoded at the primary serving site.These RCL PDUS may be processed by an RLC receiving entity operating atthe primary serving site. The RLC receiving entity at the primaryserving site may provide control information (e.g., through a networkinterface such as the X2bis) to the RLC entity handling the same logicalchannel at the secondary serving site. For example, the RLC entity atthe primary serving site that receives the RLC PDUS from the WTRU maysend information relating to the identity/sequence number of RLCs PDUsthat have and/or have not been successfully received to the RLC entityat the secondary serving site in order to allow the RLC entity at thesecondary serving site to generate and provide status reports and othercontrol information to the peer RLC entity at the WTRU side (e.g., viadownlink transmissions). In an example, RLC PDUs de-multiplexed fromuplink transport blocks received at and decoded by the secondary servingsite may be relayed to the RLC receiving entity at the primary servingsite without processing by the RLC entity at the secondary serving site.The RLC PDUs received in the UL by the secondary serving site may beforwarded to the primary serving site RLC instance for processing when apooled UL transmission scheme is utilized.

In an example, the WTRU may transmit RLC control PDUs in the uplink tothe secondary serving site, while RLC data PDUs may be transmitted tothe primary serving site. For example, RLC control PDUs generated by theRLC entity at the WTRU may be multiplexed onto transport blocksdelivered on a transport channel associated with the secondary servingsite, while RLC data PDUs may be multiplexed onto transport blocksdelivered on a transport channel associated with the primary servingsite. In an example, a given bi-directional logical channel may be splitinto two bi-directional sub-logical channels. A first sub-logicalchannel of the bi-directional logical channel may be associated with RLCdata PDUs that are transmitted by the WTRU to a first serving site(e.g., the primary serving site) and with RLC control PDUs that arereceived from the primary serving site. A second sub-logical channel ofthe bi-directional logical channel may be associated with RLC data PDUsthat are received by the WTRU from a second serving site (e.g., thesecondary serving site) and with RLC control PDUs that are transmittedto the secondary serving site.

In an example, the RLC entity may be located at the primary servingsite. For example, RLC PDUs to be transmitted in the downlink to theWTRU may be forwarded to the secondary serving site from the RLC entityin the primary serving site using a network interface (e.g., the X2bis).For example, the MAC entity in the secondary serving site may receivethe RLC PDUs from the RLC entity in the primary serving site andtransmit RLC PDUs to the WTRU over one or more secondary serving sitecells. The RLC entity located in the primary serving site may correspondto a single RLC entity that is configured to generate RLC PDUsassociated with the primary and/or secondary serving sites. In anexample, downlink data transmitted to the WTRU may be sent via thesecondary serving site, so the RLC entity located in the primary servingsite be configured to provide any RLC PDUs to be delivered to the WTRUto the secondary serving site for transmission.

Since the primary serving site may generate the RLC PDUs to be deliveredvia the secondary serving site, and the RLC entity located in theprimary serving site may not be aware of the near real-time channelconditions experienced at the secondary serving site at the time of RLCPDU generation, some segmentation and/or other scheduling decisions maybe performed at the secondary serving site after it receives RLC PDUs tobe delivered to the WTRU from the primary serving site. For example, anRLC entity located in a node that is different from the node that thatmakes the scheduling decisions for delivering the data of that RLCentity (e.g., the RLC entity is located at the primary serving site butthe MAC instance performing the scheduling is located at the secondaryserving site) may generate one or more RLC PDUs that are not of anappropriate size given the transport block size allocated by a MACinstance performing the scheduling. For example, an RLC PDU generated bythe RLC instance at the primary serving site may not fit into thetransport block size allocated by the MAC instance at the secondaryserving site. To avoid the delayed transmission of such an RLC PDU untilthe scheduler allocates a transport block that can accommodate the RLCPDU (e.g., which may be difficult given current channel conditions),techniques may be specified for avoiding situations wherein transmissionmay be delayed and/or some segmentation and/or limited RLC functionalitymay be performed at the secondary serving site even though the RLCentity is located at the primary serving site.

For example, to avoid the generation of relatively large RLC PDUs thatmay be delayed upon arriving at the MAC instance of the secondaryserving site, the RLC entity in the primary serving site may berestricted from generating RLC PDUs larger than a maximum RLC PDU size.By establishing a maximum RLC PDU size for RLC PDUs generated at an RLCentity that is located at a different serving site than the MAC instanceused to transmit the data to the WTRU, the probability that the RLC PDUsdo not fit into the transport block size set by the MAC instance of thesecondary serving site may be minimized. The maximum RLC PDU size forRLC PDUs transmitted by a serving site that is does not include the RLCentity that generated the RLC PDU may be smaller than the maximum RLCPDU size for RLC PDUs that are transmitted from the serving site thatincludes the RLC entity. In an example, RLC PDUs transmitted from aserving site that includes the RLC entity that generated the RLC PDUsmay be unrestricted in terms of a maximum RLC PDU size.

In an example, although the secondary serving site may not include afull RLC entity, RLC segmentation functionality may be located in thesecondary serving site, for example above the MAC instance associatedwith the secondary serving cell. For example, the RLC entity in theprimary serving site may be configured to initially generate RLC PDUs tobe transmitted from one or more of the primary and/or secondary servingsite. The RLC entity at the primary serving site may be configured toperform segmentation functionality of RLC PDUs transmitted over thecells belonging to the primary serving site. However, the RLC entity inthe primary serving site may be configured to refrain from segmentingRLC PDUs it generates that are to be transmitted over the cellsbelonging to the secondary serving site. The RLC segmentationfunctionality for RLC PDUs transmitted via the secondary serving sitemay be located at the secondary serving site, for example even if theremaining RLC functionality for processing those RLC PDUs is located atthe primary serving site in the network. The secondary serving site mayreceive RLC PDUs generated by the primary serving site and may segmentthe RLC PDUs to be transmitted over the MAC instance associated with thesecondary serving site. The segmentation of RLC PDUs at the secondaryserving site may be transparent to the RLC entity located at the primaryserving site.

RLC Status PDUs (e.g., RLC control PDUs including an RLC Status Report)may be sent to the RLC entity at the primary serving site. In anexample, when the RLC entity at the primary serving site receives andRLC Status PDU for an RLC PDU that has been segmented at the secondaryserving site, the RLC Status PDU may be forwarded to the secondaryserving site and/or processed by the secondary serving site. In anexample, when the RLC entity receives an RLC Status PDU that NACKs anRLC PDU that was segmented at secondary serving site, the RLC entity mayretransmit the entire original RLC PDUs even if some of the segmentshave been ACKed, so long as a segment of the original RLC PDU has beenNACKed. In this manner, the RLC status report may be processed on theprimary serving site without having any knowledge of segmentation at thesecondary serving site.

In an example, the MAC instance transmitting an RLC PDU (e.g., the MACinstance at the secondary serving site) may be configured to supportsegmentation of RLC PDUs. For example, the RLC PDUs may be generated bythe RLC entity of the primary serving site and may be forwarded to theMAC instance of a cell at the secondary serving site. Upon reception ofthe RLC PDU, the MAC instance may determine whether to performsegmentation of the RLC PDU, for example based on whether there isavailable space in the scheduled transport block. The MAC instance mayperform segmentation and concatenation of RLC PDUs. Since the receivingside MAC instance may reassemble the segments of the RLC PDU generatedby the MAC instance, additional segmentation information may be added tothe MAC header. For example, the segmentation information may provide anindication of whether the MAC PDU that includes the header includes aMAC SDU that corresponds to a full RLC PDU, a MAC SDU that correspondsto a first segment of an RLC PDU, a MAC SDU that corresponds to a middlesegment of an RLC PDU, and/or a MAC SDU that corresponds to a last orfinal segment of an RLC PDU. The MAC header may include a sequencenumber for each MAC PDU. The WTRU may reorder the MAC PDUs andreassemble the MAC SDUs, for example based on the sequence number and/orthe additional segmentation information that indicates whether the MACSDU corresponds to a fist, middle, or final segment of a given RLC PDU.In an example, MAC SDUs may be provided with sequence numbers, and theMAC header may indicate the segment number of a given MAC SDU.

Upon reception of the MAC PDU from a MAC instance of the secondaryserving site, the MAC instance at the receiving entity (e.g., the WTRU)may reassemble the segmented MAC SDUs and forward the unsegmented MACSDUs to the RLC entity. For example, based on the sequence numbers ofthe received MAC PDUs, the WTRU may re-order the received MAC PDUsand/or de-assemble the MAC PDUs. If the segmentation entity indicatesthat segmentation of MAC SDUs has been performed by the MAC entity, theWTRU may reassemble the segments included in a plurality of MAC PDUsinto a MAC SDU.

Since the RLC entity and MAC entity may not be collocated in a givennetwork node (e.g., the RLC entity may be at the primary serving siteand the MAC entity may be located at the secondary serving site) and thenetwork interface between the primary and secondary serving sites may beassociated with relatively large delays, buffering and/or flow controlmay be implemented between the secondary and primary serving sites inorder to ensure continuity of transmissions. For example, flow controlmay be performed in order for the scheduler located at the secondary MACinstance to appropriately schedule resources for transmission of RLCdata PDUs forwarded from the primary serving site. For example, the MACinstance at the secondary serving site may request information relatedto the transmission of one or more RLC PDUs from the RLC entity at theprimary serving site. As an example, the MAC instance may request one ormore of an indication of the number of bits of data that the MACinstance is scheduling for transmission to the WTRU, an indication ofthe amount of time a the requested number of bits would take to betransmitted to the WTRU, an indication of the amount of time a certainbuffer size would take to be transmitted to the WTRU, an indication ofamount of radio resources available for transmitting to the WTRU, anindication of the average data rate supported for transmitting to theWTRU, and/or a poll request of the primary serving site to determine ifthere may be available data that is to be transmitted to the WTRU.

The RLC entity at the primary serving site may be configured to providethe secondary serving site scheduler (e.g., located in the MAC instanceof the secondary serving site) with information related to the amount ofdata, type of data, and/or characteristics of the data that is to betransmitted to the WTRU. For example, the primary serving site may sendinformation related to data buffered for transmission for the WTRU tothe MAC instance at the secondary serving site (e.g., using the networkinterface). The primary serving site may provide the MAC instance of thesecondary site with a total buffer status report for DL data to betransmitted to the WTRU (e.g., data to be transmitted via either theprimary or secondary serving site). The primary serving site may providethe MAC instance of the secondary site with a buffer status report forDL data to be transmitted to the WTRU that is transmitted/mapped to thesecondary serving site. The primary serving site may send a request tothe MAC instance of the secondary site that indicates that data is to betransmitted over the secondary serving site cells. For example, therequest may indicate a total number of buffers to be transmitted overthe secondary serving site and/or desired bit rate.

The AMC instances at the different serving sites may implement differentrules for handling and processing data transmissions. For example,logical channel multiplexing, power control, rules for performing ULPUSCH transmission may be different depending on the site to be used.

As an example, radio link monitoring (RLM) may be performed by the MACinstance associated with the primary serving site (e.g., at the WTRU),but the MAC instance associate with the secondary site (e.g., at theWTRU) may refrain from performing RLM unless specifically configured bythe network to do so. In an example, detecting RLF on a primary MACinstance may lead to RRC connection re-establishment, while detectingRLF on a secondary MAC instance may not lead to RRC connectionre-establishment. In an example, a MAC reset for a secondary MACinstance may not lead to reset of another MAC instance (e.g., a primaryMAC instance and/or another secondary MAC instance). A MAC reset for asecondary MAC instance may suspend DRBs that are associated solely withthe MAC instance being resets; however, DRBs for that are associatedwith the MAC instance being reset and also with another MAC instance mayremain active, as the data may be transmitted via the other MAC instanceduring the reset procedure.

When using a MAC instance-specific DRX (e.g., different MAC instancesmay be applying different DRX configurations), the DRX state of aprimary MAC may have precedence or priority over a DRX state of asecondary MAC. For example, if a WTRU is configured to refrain fromperforming uplink transmissions in two MAC instances simultaneously, theWTRU being in DRX Active Time in a primary MAC instance may imply thatthe WTRU should be in a DRX inactive state in a secondary MAC instance.In an example, when an SR is triggered based on data becoming availablefor a given RB (e.g., DRB, SRB, etc.), the WTRU may perform an SRtransmission using the MAC instance that corresponds to the concernedRB. In an example, when an SR is triggered based on data becomingavailable for a given DRB, the WTRU may perform an SR transmission usingthe MAC instance that corresponds to the concerned DRB, but if the SRtriggered based on data to be transmitted for an SRB, the SR proceduremay be performed in the primary MAC instance (e.g., even when the SRB isassociated with the secondary MAC instance such as SRB3).

In an example, the MAC instance associated with each of the servingsites may operate relatively independent of each other. For example,multiple MAC instances (or entities) may be defined, where each MACinstance may use transport channels associated with a single servingsite. Each of the MAC instances may use an independent MACconfigurations, for example independent sets of parameters, statevariables, timers, HARQ entities, etc. Independent per-site MACoperation may apply to operation including one or more of random accessprocedures, maintenance of uplink time alignment (e.g., each MACinstance may maintain its own Active Time, DRX-related timers,DRX-related parameters, TAT timer, etc.), activation/de-activation ofScells (e.g., each MAC instance may have a Pcell and/or one or moreScells), DL-SCH data transfer, UL-SCH data transfer (e.g., schedulingrequest, buffer status reporting, power headroom reporting, logicalchannel prioritization, etc.), discontinuous reception (DRX) operation,MAC reconfiguration procedures, MAC reset procedures, semi-persistentscheduling, and/or the like.

As an example, the MAC instance at a given serving site may beconfigured to perform buffer status reporting (BSR). Differentprocedures for buffer status reporting may be applied, for example basedon the Layer 2 architecture/transmission scheme utilized in the uplink.

As an example, BSR reporting may be performed independently by differentMAC instances. For example, multiple BSR procedures may operateindependently and/or concurrently, where a given BSR procedure maycorrespond to a given serving site (e.g., and/or MAC instance). A BSRprocedure associated with a given MAC instance may operate on/beassociated with a logical channel scheduling group of the servingsite/MAC instance. A BSR report generated as part of a BSR procedureassociated with a given MAC instance may be included in a MAC controlelement that is include in a transport block for a transport channelassociated with the serving site/MAC instance. The BSR report for agiven MAC instance may be generated based on information related totransmission/reception of the concerned MAC instance (e.g., allocated ULresources, UL grant(s), MAC PDU transmission/reception, informationconsidered in the determination applicable to generating a padding BSR,the cancellation of triggered BSRs, the BSR value, etc.) but notinformation related to the transmission of other MAC instances. BSRparameters such as the BSR retransmission timer (e.g., retxBSR-Timer)and/or the periodic BSR timer (e.g., periodicBSR-Timer) may havedifferent values depending on the serving site or MAC instance the BSRparameters are associated with. Independent BSR reporting may beutilized for one or more UL transmission schemes/Layer 2 structures. Forexample, Independent BSR reporting may be utilized if a segregated ULtransmission scheme/Layer 2 structure is used. In this manner, thedifferent scheduling entities at the network side may be made aware ofthe buffer status pertaining to the logical channel scheduling group forits corresponding serving site/MAC instance.

In an example, common BSR reporting may be performed across a pluralityof MAC instances. For example, a single, combined BSR procedure mayoperate across a plurality of serving sites and/or logical channels. Acombined BSR procedure may provide each scheduler with informationrelated to transmissions at the serving site associated with thescheduler and/or information related to transmissions at other servingsites utilized by the WTRU.

For example, whenever a BSR is triggered, a BSR may be transmitted foreach serving site. The BSR for a given serving site may be transmittedover a transport channel associated with the serving site. The BSR forthe serving site may include information generated based on uplink datathat is to be transmitted to that serving site. A BSR may not betransmitted to one or more serving sites even if a BSR has beentriggered if no data is available for transmission from logical channelscheduling group associated with the serving site. A padding BSR may betransmitted for one or more serving sites, for example if the number ofpadding bits in one of the transport blocks for this serving site issufficient. The contents of the BSR transmitted for a serving site maybe determined based on the data from the corresponding logical channelscheduling group of the serving site. If data from a given logicalchannel is multiplexed on to transport blocks for more than one servingsite, the BSR may reflect the status after MAC PDUs have been generatedfor the different serving sites (e.g., so that the WTRU does not make itappear that there is more data available than actually is to betransmitted by reporting data in multiple BSRs to multiple sites).

The data considered by the WTRU to be available for transmission for thepurpose of generating a BSR may include one or more of RLC SDUs, RLCdata PDUs, segments of RLC data PDUs, and/or RLC status PDUs associatedwith the logical channel scheduling group of the MAC instance for whichthe BSR is being generated. PDCP SDUs and/or PDCP PDUs may not beconsidered for BSR generation. By considering RLC SDUs, RLC data PDUs,and/or RLC status PDUs associated with the logical channel schedulinggroup of the MAC instance for which the BSR is being generated as beingavailable for transmission, the BSR status reporting may be effectivelyimplemented in a split RLC transmission scheme/Layer 2 structure.

In an example, the data considered available for transmission for thepurpose of BSR generation may include a portion or all PDCP SDUs and/orPDCP PDUs, for example PDCP SDUs and/or PDCP PDUs that may be consideredavailable as per a Release 11 procedure. If a portion of the PDCP SDUsand/or PDCP PDUs are considered available, the portion may correspond toa ratio provided by higher layers. The portion may correspond to thegreater of a “resource utilization ratio” of the serving site (or MACinstance) and a minimum value. The “resource utilization ratio” maycorrespond to a ratio of the UL resources allocated within a given timeperiod for transport channels associated with the corresponding servingsite/MAC instance) and the sum of all UL resources allocated within thesame time period for transport channels associated with all servingsites/MAC instances. In an example, PDCP SDUs and/or PDCP PDUs may beconsidered available for transmission in the BSR generation procedure ifthe PDCP SDUs and/or PDCP PDUs are associated with the specific servingsite/MAC instance for which the transmission is being generated. PDCPSDUs and/or PDCP PDUs associated with other sites (e.g., sites that arenot associated with the BSR being generated) may not be countedavailable for transmission in the BSR calculation of another servingsite.

The data considered available for transmission may include a portion ofthe total amount of data considered available for transmission for alogical channel in given logical channel scheduling group. If a portionof the PDCP SDUs and/or PDCP PDUs are considered available, the portionmay correspond to a ratio provided by higher layers. The portion maycorrespond to the greater of a “resource utilization ratio” of theserving site (or MAC instance) and a minimum value.

A WTRU may be configured with one or more sets of resource for sendingscheduling requests (SRs) to the network. For multi-layer operation, theWTRU may be allocated resources for performing SRs in multiple layers(e.g., a first resource may be available in a primary layer and a secondresource may be available in a secondary layer). An example of aresource that may be used for transmitting SRs to the network may be aPRACH configuration for random access-scheduling request (RA-SRs).Another example of a resource that may be used for transmitting SRs maybe a received Physical Uplink Control Channel (PUCCH) configuration thatis received by the WTRU (e.g., via RRC signaling) that allocatesdedicated PUCCH resources to a given WTRU for send scheduling requests(e.g., a dedicated SR (D-SR) resources). The PUCCH configuration maydefine a periodic allocation of PUCCH physical resources that the WTRUmay use for sending SRs on a given layer. In an example, the WTRU mayselect a resource to use for performing a SR based on one or morecharacteristics of the data to be transmitted. For example, an exampleof a data characteristic that may be used to select an appropriateresource for sending a SR may include the identity of the bearer (e.g.,a DRB, a SRB, etc.) associated with the data to be transmitted. Anotherexample of a data characteristic that may be used to select anappropriate resource for sending a SR may include the association of agiven bearer with a specific layer (e.g., a primary layer, a secondarylayer, etc.).

As an example, a WTRU may be configured with a PRACH configuration for aPCell of a primary layer. The WTRU may also be configured with a PRACHconfiguration for a serving cell of a secondary layer. Further, the WTRUmay be configured with a dedicated resource for sending SRs on PUCCH inone or more layers, for example in a serving cell of the secondarylayer. The WTRU may be configured with a first DRB and/or a first SRBthat may be associated with the primary layer. The WTRU may beconfigured with a second DRB and/or a second SRB that may be associatedwith the secondary layer. If new data becomes available for transmissionfor one or more of the RBs configured for the WTRU and a SR istriggered, the WTRU may select a resource to use to perform the SRprocedure based on the layer associated with the RB that triggered therequest. For example, if the SR was triggered from data on the firstSRB, the WTRU may perform RA-SR on the PCell of the primary layer. Ifthe SR was triggered from data associated with the second DRB, the WTRUmay perform a D-SR and/or a RA-SR on the serving cell of the secondarylayer.

In an example, the WTRU may be configured to perform a SR procedure inthe PCell of a primary layer following the failure of SR procedure in asecondary layer. For example, when sending a SR on the primary layer foran RB associated with a secondary layer, the WTRU may send an indicationof the data available for both RBs associated with the secondary layer(e.g., that triggered the SR) and any data available for transmissionassociated with an RB mapped to the primary layer in the BSR. In anexample, the WTRU may re-associate one or more RBs associated with thesecondary layer to the primary layer based on an SR failure in thesecondary layer.

In an example, how the WTRU handles an SR failure may be based on whichlayer included the SR resource used for the failed SR procedure (e.g.,primary layer, secondary layer, etc.) and/or the type of SR resourceused for the failed SR procedure (e.g., RA-SR, D-SR, etc.). For example,when the WTRU determines that a D-SR procedure has failed using PUCCHresources of a cell of a secondary layer, the WTRU may be configured toinitiate a RA-SR procedure in a cell of a secondary layer. For example,the cell used for the RA-SR in the secondary layer may be the same cellas was used for the D-SR procedure that failed or may be a differentcell of the secondary layer (e.g., the WTRU may try the same cell first,then a different cell of the secondary layer). If the WTRU determinesthat the RA-SR also fails for the secondary layer, the WTRU may theninitiate SR procedure on the PCell of the primary layer. The SR on thePCell of the primary layer may be performed according to the SRconfiguration for the WTRU in the PCell. For example, if the WTRU hasbeen configured with dedicated PUCCH resources for sending SRs in thePCell, a D-SR procedure may be performed. If the WTRU has not beenconfigured with dedicated PUCCH resources for SR in the PCell, the WTRUmay initiate a RA-SR procedure. If the SR procedure(s) in the PCell ofthe primary layer fail, the WTRU may attempt to re-establish the RRCconnection with the PCell of the primary layer. In another example, ifany SR procedure (e.g., D-SR or RA-SR) fails on the secondary layer, theWTRU may attempt to perform a SR procedure in the PCell of the primarylayer (e.g., rather than attempting to first perform a different type ofSR procedure in the secondary layer).

In an example, the WTRU may be configured to perform a SR procedure(e.g., a RA-SR procedure) in the primary layer based on the data thattriggered the SR being associated with a RB of the secondary layer. Forexample, a RA-SR procedure in the primary layer may be used for SRs fordata associated with RBs in the secondary layer. The WTRU may indicatein the RA-SR procedure that the data is associated with an RB mapped tothe secondary layer. In an example, the WTRU may initiate a mobilityprocedure based on an SR failure in the secondary layer. For example, ifan SR procedure fails in the secondary layer, the WTRU may be configuredto perform a re-association procedure (e.g., RRC reconfigurationprocedure) for one or more radio bearers that moves the RBs associatedwith the layer that the SR failed on to a different layer (e.g. theprimary layer). In an example, the WTRU may determine that UL RLF hasoccurred on given layer upon RACH failure using PRACH resources of theconcerned layer (e.g., for a SR procedure). For example, for an SRfailure corresponding to a secondary layer, the WTRU may initiate abearer mobility-related procedure in a different layer (e.g., a primarylayer).

A WTRU may utilize different procedures for maintaining timing alignmentof the different layers. For example, the timing alignment (TA)procedures utilized in a given cell (e.g., a PCell) may be based onwhich layer the TA procedure is associated with. For example, the WTRUmay perform various actions regarding timing alignment in a first cellof a first layer (e.g., a PCell of the primary layer) based on detectingone or more conditions associated with a second cell in a second layer(e.g., a cell in a secondary layer). For example, a SR failure in asecondary layer may trigger one or more actions related to TA in theprimary layer.

As an example, the WTRU may consider the timing alignment timer (TAT)(e.g., some or all applicable TATs, for example if multiple TA Groupsare configured) associated with a given layer to have expired upondetecting a D-SR failure and/or a RA-SR failure in that layer. Forexample, the WTRU may consider the TAT of the PCell of a secondary layerto have expired based on determining that a SR procedure has failedusing a resource of the PCell of the secondary layer.

In an example, TAT expiration (e.g., or a trigger that causes the WTRUto deem the TAT to have expired) in a first cell of a first layer maytrigger an extended SR/BSR to be sent in another cell associated with adifferent layer. For example, if the WTRU determines that the TATassociated with one or more cells (e.g., the PCell) of a secondary layerhas expired and/or has been deemed to have expired (e.g., based on an SRfailure), the WTRU may send a BSR to a cell of the primary layer (e.g.,the PCell of the primary layer). For example, the BSR sent via theprimary layer may include information regarding any data for RBsassociated with the secondary layer to be transmitted in addition to anydata associated with RBs of the primary layer that is to be transmitted.

In an example, TAT expiration (e.g., or a trigger that causes the WTRUto deem the TAT to have expired) may trigger RB mobility to anotherlayer and/or RB suspension. For example, the WTRU may re-associate oneor more RBs associated with a layer that includes a cell for which theTAT expired (e.g., or was deemed to have expired) to a different cell ina different layer (e.g., to the primary layer). In an example, RBassociation may be performed when all TATs applicable to a secondarylayer have expired or have been deemed to have expired. In such a case,if the TAT has expired on a first cell of a secondary layer but that TATof a second cell has not yet expired, the WTRU may refrain fromperforming RB mobility to another layer until the TAT of the second cellexpires or is deemed to have expired. If an RB is re-associated to adifferent layer, once one or more TATs are started or running in thesecondary layer, the WTRU may reconfigure the RBs that were moved to bere-associated with the secondary layer. In an example, RB suspension maybe performed by the WTRU when all TATs applicable to a secondary layerhave expired or have been deemed to have expired. In such a case, if theTAT has expired on a first cell of a secondary layer but that TAT of asecond cell has not yet expired, the WTRU may refrain from suspendingthe RB. If the WTRU does suspend an RB based on the expiration of allTATs associated with a given layer, once the WTRU determines that atleast one TAT applicable to a secondary layer has been started and/or isnow running, the WTRU may consider the concerned RBs as active

In an example, TAT expiration (e.g., or a trigger that causes the WTRUto deem the TAT to have expired) may trigger deactivation of MACinstance/layer associated with the expired TAT. For example, if the WTRUdetermines that a TAT associated with one or more cells (e.g., a PCell)of a secondary layer has expired or has been deemed to have expired, theWTRU may deactivate some or all cells of the concerned MAC instance. Inan example, TAT expiration (e.g., or a trigger that causes the WTRU todeem the TAT to have expired) may trigger the WTRU to suspend one ormore layer-specific radio bearers. For example, if the WTRU determinesthat a TAT associated with one or more cells (e.g., a PCell) of asecondary layer has expired or has been deemed to have expired, the WTRUmay suspend one or more radio bearers associated with the concernedlayer. In an example, TAT expiration (e.g., or a trigger that causes theWTRU to deem the TAT to have expired) may trigger the WTRU to perform amobility procedure that moves/re-associates one or more layer-specificbearers to a different layer. For example, For example, if the WTRUdetermines that a TAT associated with one or more cells (e.g., a PCell)of a secondary layer has expired or has been deemed to have expired, theWTRU may initiate a mobility procedure in order to reconfigure radiobearers to be re-associated with a different layer (e.g., a primarylayer).

In an example, TAT expiration (e.g., or a trigger that causes the WTRUto deem the TAT to have expired) may trigger a switch of the active MACinstance/layer. For example, if the WTRU determines that a TATassociated with one or more cells (e.g., a PCell) of a secondary layerhas expired or has been deemed to have expired, the WTRU may initiate aprocedure to activate one or more cells (e.g., a PCell) of a primary MACinstance, for example if the primary MAC instance had been deactivated.

Layer 1 (e.g., PHY layer) and/or Layer 2 (e.g., MAC, RRC, etc.) basedcontrol of dynamic Radio Resource Management (RRM) may be performed inorder to coordinate multi-layer RRM. For example, the control and theallocation of physical layer resources for each layer may be a complexand may depend on the type of control plane architecture that isutilized (e.g., distributed control plane, coordinated control plane,centralized control plane, etc.). For example, a WTRU may be configuredwith dual connectivity such that the SRBs are terminated in a singlelayer (e.g., the primary layer) and/or one or more layers may have noSRB terminated in the serving site for the layer. In such a case,configuration information and other control data to support RRM may bedetermined for a layer (e.g., a secondary layer/SCeNB layer) by one ormore of a RCNC (e.g., which may be located at the MeNB), another layerserving site (e.g., the MeNB), and/or by serving site of the concernedlayer (e.g., the SCeNB). The configuration information may be providedto the appropriate network node where the SRB terminates over one ormore interfaces between the layers (e.g., the X2bis). For example, theWTRU may be configured such that SRBs terminate in the MeNB, but controlinformation for the SRB may be provided to other serving sites (e.g.,SCeNB).

However, in some scenarios the latency of inter-layercommunications/interfaces may be problematic for RRM. For example, RRMand/or reconfiguration in at a secondary layer (e.g., associated with aSCeNB) may be complicated by the fact that an interface between theserving site of the macro layer where an SRB may be terminated (e.g.,MeNB) and the serving site of the secondary layer (e.g., SCeNB) may beassociated with a relatively high latency and/or may introduce arelatively large delay. Reducing latency for the reconfiguration of aMAC instance and PHY configuration of a layer while still providing forscheduler flexibility (e.g., in terms of allocation of resources) may berelevant to several scheduling functions, such as one or more oftransmission time interval (TTI) bundling, PUCCH allocation for D-SR,CQI reporting, hybrid automatic repeat request (HARQ) feedback (e.g.,including HARQ format), allocation of sounding reference signal (SRS)resources, configuration reference signals, etc. For example, parametersincluded in one or more IEs such as sps-Config, mac-MainConfig (e.g.,including ttiBundling, drx-Config, etc.), physicalConfigDedicated (e.g.,including pucch-ConfigDedicated, cqi-ReportConfig,soundingRS-UL-ConfigDedicated, schedulingRequestConfig,cqi-ReportConfig-r10, csi-RS-Config-r10,soundingRS-UL-ConfigDedicatedAperiodic-r10, csi-RS-ConfigNZP, etc.) maybe time sensitive and delays in signaling and/or configuring suchparameters may be problematic.

As an example, the synchronization of a reconfiguration instant (e.g.,the time at which a new configuration should start being applied) may bedifficult to achieve in a multi-layer setting, for example ifintra-network communications between serving sites is associated with ahigh latency and the control plane (e.g., and/or a specific SRB) isterminated at one of the layers. For example, if the WTRU receives anRRC reconfiguration message that reconfigures one or more aspectsrelated to connectivity at a secondary layer (e.g., associated with anSCeNB), timing and/or synchronization between the scheduler in thesecondary layer and the MAC instance associated with the secondary layerin the WTRU may be challenging. For example, the WTRU may be configuredto determine a fixed point in time from which the new configuration isassumed to be valid.

Timing and synchronization may be an issue at the network side as well,for example where the network is attempting to reallocate resources fromone WTRU to another, as the network may have to determine the firstpossible occasion from which such resources may be available forallocation to given WTRU. For example, the network may attempt todetermine when resources may be available at a given WTRU for thepurpose of deactivating TTI Bundling, releasing PUCCH resources forD-SR, allocating CQI reporting instance, receiving HARQ feedback (e.g.,including HARQ format), determining when to apply a new DRXconfiguration, releasing SRS resources, modifying reference signals,and/or the like. For example, the network may attempt to determine whena WTRU can and/or will begin applying one or more parameters included inIEs such as sps-Config, mac-MainConfig (e.g., including ttiBundling,drx-Config, etc.), physicalConfigDedicated (e.g., includingpucch-ConfigDedicated, cqi-ReportConfig, soundingRS-UL-ConfigDedicated,schedulingRequestConfig, cqi-ReportConfig-r10, csi-RS-Config-r10,soundingRS-UL-ConfigDedicatedAperiodic-r10, csi-RS-ConfigNZP, etc.).Timing for activation and deactivation of semi-persistent scheduling(SPS) resources may be controlled using PHY layer control signaling(e.g., activated and deactivate via PDCCH orders).

For example, the WTRU and one or more serving sites may be configured toestablish a one or more preconfigurations for a set of parameters, mayassign an index to each preconfigured set of parameters, and may utilizeexplicit control signaling and/or implicit rules to switch the activeconfiguration (e.g., activate and/or deactivate a given set ofparameters). For example, the WTRU and/or serving sites of differentlayers may utilize local, flexible, and/or dynamic management ofphysical layer resources for a given layer and/or scheduler (e.g., for aSCeNB) without having to introduce and/or utilize an RRC component witha SRB termination in the layer for which the configuration is beingestablished (e.g., secondary layer with an SCeNB serving site).

For example, rather than or in addition to relying on RRC signaling forconfiguring static parameters for RRM (e.g., which may be used forlayers where one or more SRBs are terminated in a RRC component at theserving site), whereby a scheduler for a given layer (e.g., in a SCeNB)may preconfigure various RRM configurations (e.g., via RRC signaling orthe like), and may signal which preconfigured allocation to use (e.g.,via PHY or MAC signaling; based on implicit rules, based on triggeringevents, etc.).

Various techniques may be used to configure the plurality of sets of RRMparameters. When used herein, the term RRM parameters may refer to oneor more of parameters related TTI bundling, PUCCH allocation for D-SR,DRX, SR, CQI reporting, HARQ feedback (e.g., including HARQ format),allocation of SRS resources, configuration reference signals, other PHYlayer parameters, and/or the like. For example, RRM parameters mayinclude one or more items of information that may be include in IEs suchas sps-Config, mac-MainConfig (e.g., including ttiBundling, drx-Config,etc.), physicalConfigDedicated (e.g., including pucch-ConfigDedicated,cqi-ReportConfig, soundingRS-UL-ConfigDedicated,schedulingRequestConfig, cqi-ReportConfig-r10, csi-RS-Config-r10,soundingRS-UL-ConfigDedicatedAperiodic-r10, csi-RS-ConfigNZP, etc.).Additionally, various subsets of RRM parameters/configurations may betreated and/or handled independently/separately. For example, sets ofSPS parameters may be preconfigured separately from sets of physicallayer configuration parameters. Similarly, sets of DRX parameters may behandled separately from sets of CQI reporting parameters. Parametersrelated to one or more different control functions may be grouped intopre-configuration groups (e.g., DRX parameters grouped with TTIparameters, CQI reporting parameters may be grouped with D-SRconfiguration parameters, etc.). When used herein, the term RRMparameters may be used to refer to one or more parameters describedabove (or similar) either alone or in various combinations. The term RRMconfiguration may refer to a group of one or more RRM parameters thatmay be grouped for preconfiguration and/or may be activated together.

For example, the WTRU may receive RRC signaling (e.g., a RRC ConnectionReconfiguration message) that configures a one or more sets of RRMparameters. The WTRU may receive a configuration with one or moreindexed set of parameters. For example, the WTRU may be preconfiguredwith one or more sets of physical layer configuration parameters (e.g.,physicalConfigDedicated) and/or one or more sets of MAC configurationparameters (e.g., mac-MainConfig). For example, each configuration maybe grouped as a separate item (e.g., a defaultConfig, and zero of morealternativeConfig). In an example each received configuration may beassociated with an index value, which may be assigned when theconfiguration is received and/or may be implicitly determined. Forexample, each configuration value may be provided in order if increasingindex number (e.g., first configuration in the message has index 0,second configuration has index 1, and so on). One or more of theconfigurations may be a default configuration. For example, the receivedreconfiguration message may explicitly indicate which received set ofparameters (e.g., configuration) is considered the default configurationand/or the first configuration and/or the configuration assigned index 0and/or the first configuration that is applied in the cell may beconsidered the default configuration. Received RRM configurations may bespecific to a certain cell or may be common across a plurality of cells.Received RRM configurations may be specific to a certain layer or may becommon across a plurality of layers. Upon receiving the plurality setsof parameters (e.g., plurality of sets of RRM configurations), the WTRUmay complete the reconfiguration by applying the parameterscorresponding to a default set.

As an example, a WTRU may receive a configuration with sets ofparameters grouped as one or more virtual cells. For example, the WTRUmay receive one or more sets of RRM parameters, for example one or moresets of physical layer configurations. The configuration may be receivedsuch that the configuration corresponds to a virtual cell. A virtualcell may be associated with a similar configuration as a traditionalcell, although the configuration may be activated and/or deactivateddynamically. For example, the WTRU may receive multiple virtual cellconfigurations (e.g., a plurality of sets of RRM parameters where eachset corresponds to a different virtual cell) for a given sCellIndex, agiven physCellId, a given dl-CarrierFreq, and/or the like. The receivedvirtual cell configurations may correspond to multiple potentialconfigurations that may be applied in a given cell. In an example, eachvirtual cell configuration and/or each set of RRM parameters may beassigned a virtualCellId for purposes of identification. The identifier(e.g., virtualCellId) may be explicitly signaled and/or may beimplicitly determined. For example, each virtual cell configuration maybe provided in order if increasing identification number (e.g., firstconfiguration in the message has virtualCellId 0, second configurationhas virtualCellId 1, and so on). One or more of the virtual cellconfigurations may be a default configuration. For example, a receivedreconfiguration message may explicitly indicate which received virtualcell configuration is considered the default configuration and/or thefirst configuration and/or the configuration assigned virtualCellId 0,and/or the first virtual cell configuration that is applied in the cellmay be considered the default configuration. Virtual cell configurationsmay be specific to a certain cell or may be common across a plurality ofcells. Virtual cell configurations may be specific to a certain layer ormay be common across a plurality of layers. Upon receiving the virtualcell configurations, the WTRU may complete the reconfiguration byapplying the parameters corresponding to a default virtual cellconfiguration.

Control signaling may be used to activate an RRM configuration and/orvirtual cell configuration, deactivate an RRM configuration and/orvirtual cell configuration, change an RRM configuration and/or virtualcell configuration, remove an RRM configuration, and/or virtual cellconfiguration, and/or the like. For example, control signaling mayapplicable to one or more cells within a layer (e.g., perhaps groups orsubsets of cells within a layer), to a specific type of cell within alayer (e.g., PCell, SCell(s), etc.), to a Timing Alignment Group (TAG),etc.

For example, physical layer signaling may be used to activate an RRMconfiguration and/or virtual cell configuration, deactivate an RRMconfiguration and/or virtual cell configuration, change an RRMconfiguration and/or virtual cell configuration, remove an RRMconfiguration, and/or virtual cell configuration, and/or the like. As anexample, physical layer signaling used for layer activation, PCellactivation, SCell activation, etc. may also include an indication of anappropriate RRM configuration and/or virtual cell configuration thatshould be applied. In an example, separate physical layer signaling maybe used to indicate which RRM configuration and/or virtual cellconfiguration should be applied in the cell, in the layer that includesthe cell, in another cell in the layer that includes the cell, inanother layer, in another cell of another layer, in a TAG, and/or thelike.

For example, once configured with a plurality of RRM configurationsand/or a plurality of virtual cell configurations for a given cell, agiven group of cells, a given layer, etc., the WTRU may receive controlsignaling, for example on the PDCCH and/or the enhanced PDCCH (ePDCCH),that activates a given RRM configuration and/or virtual cellconfiguration. For example, the WTRU may receive an index and/orvirtualCellId corresponding to a given RRM configuration and/or virtualcell configuration in a downlink control information (DCI) field and/orvia other physical layer signaling.

For example, the WTRU may receive a DCI that activates a RRMconfiguration and/or virtual cell configuration for a one or more cells,and the WTRU may determine which RRM configuration and/or virtual cellconfiguration to apply based on one or more of an explicit index and/orvirtual cell identity indicated in the DCI, the identity of the searchspace in which the DCI was successfully decoded (e.g., each search spaceand/or portions of a search space may be implicitly mapped to a givenindex and/or virtual cell), the radio network temporary identifier(RNTI) used to decode the DCI (e.g., each RRM configuration and/orvirtual cell configuration may be assigned an RNTI and/or an implicitmapping may be assumed based on which RNTI is used), the identity of thefirst (or last or some other CCE in the range used for decoding the DCI)control channel element (CCE) associated with the DCI (e.g., CCEs may beimplicitly mapped to RRM configurations and/or virtual cellconfigurations), and/or the like.

Physical layer signaling may indicate the activation and/or deactivationof a RRM configuration and/or virtual cell configuration, for example byincluding the corresponding index and or virtual cell identity in thesignaling format. If the WTRU is operating using a non-default RRMconfiguration and/or virtual cell configuration, the non-default RRMconfiguration and/or virtual cell configuration is deactivated and/orremoved, the WTRU may implicitly determine use the default RRMconfiguration and/or virtual cell configuration for the concerned layer(e.g. a configuration with index/virtualCellId 0) unless a different RRMconfiguration and/or virtual cell configuration is explicitly indicated.

Feedback may be sent by the WTRU to confirm reconfiguration. Forexample, the WTRU may transmit feedback to indicate the successfulcompletion of the reconfiguration and/or that physical layer signalingwas successfully received. For example, the WTRU may transmit HARQACK/NACK for the received physical layer signaling used to activateand/or deactivate a RRM configuration and/or virtual cell configuration.For example, positive feedback (e.g., ACK) may indicate successfulreception physical layer signaling that changed the RRM configurationand/or virtual cell configuration. For example, the HARQ ACK/NACKfeedback may be transmitted a fixed time after successful reception ofthe control signaling. The ACK/NACK feedback may be transmitted usingthe RRM configuration and/or virtual cell configuration that had beenpreviously applicable at the time of reception of the physical layersignaling that changed the RRM configuration and/or virtual cellconfiguration (e.g., in subframe n) of the control signaling thatchanged the configuration. For example, if the physical layer controlsignaling was received in subframe n, the feedback may be transmitted insubframe n+4.

In an example, the feedback for the HARQ ACK/NACK for the receivedphysical layer signaling used to activate and/or deactivate a RRMconfiguration and/or virtual cell configuration may be transmitted usingthe RRM configuration and/or virtual cell configuration indicated in thephysical layer control signaling. For example, ACK/NACK feedback may betransmitted using the new RRM configuration and/or virtual cellconfiguration in subframe n+(reconfigurationDelay). ThereconfigurationDelay may be a configurable aspect (e.g., that may beindicated in the physical layer activation signaling and/or may bepreconfigured with the RRM/virtual cell configuration set) or may beequivalent to some fixed processing delay (e.g., 15 ms). In an example,physical layer signaling used to activate and/or deactivate a RRMconfiguration and/or virtual cell configuration may indicate a specificresource for the transmission of ACK/NACK feedback. In an example, theWTRU may transmit a first feedback indicating whether the physical layersignaling used to activate and/or deactivate a RRM configuration and/orvirtual cell configuration was successfully received (e.g., using amethod described herein), and a second feedback to indicate thesuccessful completion of the reconfiguration as indicated by the controlsignaling (e.g., using a method described herein). In an example, theconfirmation of the successful reconfiguration to the new RRMconfiguration and/or virtual cell configuration may be performed bytransmission of a random access preamble. For example, one the WTRUsuccessfully applies the new RRM configuration and/or virtual cellconfiguration, the WTRU may initiate a RACH procedure. A msg3 mayinclude a MAC CE that indicates the activated RRM configuration and/orvirtual cell configuration.

Layer 2 signaling such as MAC signaling may be used to activate an RRMconfiguration and/or virtual cell configuration, deactivate an RRMconfiguration and/or virtual cell configuration, change an RRMconfiguration and/or virtual cell configuration, remove an RRMconfiguration, and/or virtual cell configuration, and/or the like. Forexample, MAC signaling used for layer activation, PCell activation,SCell activation, etc. may also include an indication of an appropriateRRM configuration and/or virtual cell configuration that should beapplied.

For example, the WTRU may receive a MAC control element (CE) thatactivates a given RRM configuration and/or virtual cell configuration.For example, the WTRU may receive an index and/or virtualCellIdcorresponding to a given RRM configuration and/or virtual cellconfiguration in a field of the MAC CE. In an example, the MAC CE usedto activate a given RRM configuration and/or virtual cell configurationmay include a bitmap, and each bit of the bitmap may correspond to agiven RRM configuration and/or virtual cell configuration. For example,the first bit of the bitmap may correspond to index/virtual cellidentity 0, the second bit of the bitmap may correspond to index/virtualcell identity 1, and so one. A 1 may indicate that the corresponding RRMconfiguration and/or virtual cell configuration is being activated, anda 0 may indicate that the corresponding RRM configuration and/or virtualcell configuration is being deactivated (or vice versa).

In an example, the WTRU may receive a MAC activation/deactivation CEthat activates and/or deactivates a layer, activates and/or deactivatesa cell in a layer, activates and/or deactivates a group of cells in alayer, etc. The MAC activation/deactivation CE may include an explicitan index and/or virtualCellId corresponding to a given RRM configurationand/or virtual cell configuration for an activated cell, group of cells,and/or layer. At bitmap as described herein may also be used.

In an example, the WTRU may receive a MAC RRMConfig CE for a specificcell, group of cells, and/or layer. The MAC RRMConfig CE may include anexplicit an index and/or virtualCellId corresponding to a given RRMconfiguration and/or virtual cell configuration for a configured cell,group of cells, and/or layer. At bitmap as described herein may also beused.

Irrespective of the signaling method used, if the WTRU is operatingusing a non-default RRM configuration and/or virtual cell configuration,the non-default RRM configuration and/or virtual cell configuration isdeactivated and/or removed (e.g., via MAC signaling), the WTRU mayimplicitly determine use the default RRM configuration and/or virtualcell configuration for the concerned cell/group of cells/layer (e.g. aconfiguration with index/virtualCellId 0) unless a different RRMconfiguration and/or virtual cell configuration is explicitly indicated.

Feedback may be sent by the WTRU to confirm reconfiguration received viaMAC signaling. For example, the WTRU may transmit feedback to indicatethe successful completion of the reconfiguration and/or that MAC CE wassuccessfully received. As an example, the feedback may be included in aMAC CE and/or on the PUCCH (e.g., a fixed time after transmission of theHARQ ACK for the transport block in which the L2/MAC signaling wasreceived).). In an example, the confirmation of the successfulreconfiguration to the new RRM configuration and/or virtual cellconfiguration may be performed by transmission of a random accesspreamble. For example, one the WTRU successfully applies the new RRMconfiguration and/or virtual cell configuration, the WTRU may initiate aRACH procedure. A msg3 may include a MAC CE that indicates the activatedRRM configuration and/or virtual cell configuration.

Implicit rules may be used to activate an RRM configuration and/orvirtual cell configuration, deactivate an RRM configuration and/orvirtual cell configuration, change an RRM configuration and/or virtualcell configuration, remove an RRM configuration and/or virtual cellconfiguration, and/or the like. For example, once preconfigured with aplurality of RRM configurations and/or virtual cell configurations for agiven cell, group of cells, layer, etc., the WTRU may determine eventsor trigger that may activate and/or deactivate an RRM configurationand/or virtual cell configuration.

For example, the WTRU may receive control signaling (e.g., a MACactivation/deactivation CE) that activates a cell, a group of cells, alayer, etc. that was preconfigured for use by the WTRU. The WTRU mayimplicitly determine that the default RRM configuration and/or virtualcell configuration for the concerned cell, a group of cells, a layer,etc. should be applied absent explicit signaling to the contrary.

The WTRU may be configured to maintain a validity timer for the activeRRM configuration and/or virtual cell configuration (e.g., for anon-default RRM configuration and/or virtual cell configuration). Forexample, the WTRU may start a validity timer for a given RRMconfiguration and/or virtual cell configuration upon receivingactivating the RRM configuration and/or virtual cell configurationand/or upon receiving the explicit control signaling that activates theRRM configuration and/or virtual cell configuration. The WTRU maydeactivate an RRM configuration and/or virtual cell configuration for agiven cell, a group of cells, a layer, etc. upon the expiration of thevalidity timer of such RRM configuration and/or virtual cellconfiguration. In an example, there may be no validity timer for adefault configuration. A validity timer may be restarted upon receptionof signaling that reactivates the RRM configuration and/or virtual cellconfiguration.

In an example, expiration of the TAT for a cell, group of cells, layer,etc. may deactivate and/or remove an RRM configuration and/or virtualcell configuration. For example, the WTRU may be configured todeactivate a RRM configuration and/or virtual cell configuration for agiven cell, group of cells, layer, etc. upon expiration of theapplicable TAT. In an example, expiration of the TAT may cause the WTRUto deactivate a non-default RRM configuration and/or virtual cellconfiguration, but not the default RRM configuration and/or virtual cellconfiguration.

The WTRU may deactivate a RRM configuration and/or virtual cellconfiguration for a given cell, group of cells, layer, etc. upondetection of radio link failure conditions for the concerned cell, groupof cells, layer, etc. In an example, detection of radio link failure maycause the WTRU to deactivate a non-default RRM configuration and/orvirtual cell configuration, but not the default RRM configuration and/orvirtual cell configuration.

The WTRU may deactivate a RRM configuration and/or virtual cellconfiguration for a given cell, group of cells, layer, etc. upondetermining that the concerned cell, group of cells, layer, etc. is inDRX (e.g., long DRX) and that z DRX period(s) have elapsed where x maybe a configuration aspect. In an example, determining that the concernedcell, group of cells, layer, etc. is in DRX (e.g., long DRX) and that zDRX period(s) have elapsed may cause the WTRU to deactivate anon-default RRM configuration and/or virtual cell configuration, but notthe default RRM configuration and/or virtual cell configuration.

e WTRU may deactivate a RRM configuration and/or virtual cellconfiguration for a given cell, group of cells, layer, etc. upondeactivating (e.g., implicitly and/or explicitly) the concerned cell,group of cells, layer, etc. (e.g., when it deactivates the cell, or thelayer in question). In an example, deactivation of the concerned cell,group of cells, layer, etc. may cause the WTRU to deactivate anon-default RRM configuration and/or virtual cell configuration, but notthe default RRM configuration and/or virtual cell configuration.

The WTRU may revert to a default RRM configuration and/or virtual cellconfiguration upon implicit and/or explicit deactivation of anon-default RRM configuration and/or virtual cell configuration (e.g.,unless some other RRM configuration and/or virtual cell configuration isexplicitly indicated). The UE may use control signaling (e.g., a RRCmessage, a MAC CE that indicates the active configuration) thatindicates that the WTRU lacks a valid configuration and/or thatindicates that a different configuration is now being used (e.g., adefault configuration).

Timing of completion of the reconfiguration to a different RRMconfiguration and/or virtual cell configuration may be specified. Forexample, the WTRU may attempt to complete the reconfiguration within xsubframe(s). The value x may be fixed (e.g., a 15 ms processing time)and/or the value x may be configured as part of the RRM configurationand/or virtual cell configuration. In an example, the delay may bedetermined beginning from the subframe n at which the applicable controlsignaling that activates the RRM configuration and/or virtual cellconfiguration is received (e.g., L1/L2 signaling). In an example, thedelay may be determined beginning from the time at which feedback forthe applicable control signaling is transmitted (e.g., L1/L2 signaling).In an example, the delay may be determined beginning from the time atwhich a confirmation of successful reconfiguration is transmitted.

Possibly, during the period [n, n+x], the WTRU may not receive the PDCCHand/or ePDCCH. In an example, the WTRU may begin using a new RRMconfiguration and/or virtual cell configuration as soon as it is able toreconfigure its transceiver, and may begin receiving the PDCCH and/orePDCCH and/or may perform uplink transmission using the configurationapplicable at the moment of reception of the concerned controlsignaling. In an example, the WTRU may be allowed to begin using the newRRM configuration and/or virtual cell configuration after thetransmission of the acknowledgement of the reception of the controlsignaling (e.g., subframe n+4).

In an example, one or more of the methods described herein may becombined in order to provide flexible RRM control by a scheduler in anode without SRB termination. For example, a WTRU may receive an RRCConnection Reconfiguration message. The RRC Connection reconfigurationmessage may be associated with/transmitted via an SRB that is terminatedat an RRC entity in the MeNB. The RRC Connection Reconfiguration messagemay add, modify, remove, etc. one or more cells associated with asecondary layer (e.g., the serving site for the secondary layer may bean SCeNB). The reconfiguration message may include a plurality of RRMconfigurations and/or virtual cell configurations for the one or morecells being added and/or modified (e.g., and possibly for the deletedcells) in the secondary layer. The various RRM configurations and/orvirtual cell configurations may be indexed and/or one or more RRMparameters within the RRM configurations and/or virtual cellconfigurations may be indexed. One of the RRM configurations and/orvirtual cell configurations may be considered a default configurationand/or one or more RRM parameters within the RRM configurations and/orvirtual cell configurations may be considered a default parameter value.The initially configured RRM configuration and/or virtual cellconfiguration may be considered the default configuration and/or theinitially configured RRM parameters may be considered the defaultparameters. The default RRM configuration and/or virtual cellconfiguration and/or the default RRM parameters may be explicitlyindicated, for example by associating them with index 0 and/or listingthem first. Grouping of configuration aspects using a virtual cell. Forexample, multiple serving cell configurations may be given for a givencarrier frequency.

The WTRU may receive Layer 1 (e.g., PHY) and/or Layer 2 (e.g., MAC)signaling (e.g., DCI on PDCCH, MAC CE, etc.) that may indicate an indexfor one or more RRM configurations and/or virtual cell configurations toapply and/or one or more RRM parameters to apply. The WTRU mayacknowledge reception at subframe n of such control signaling (e.g.,perhaps including an indication of the configuration index in thefeedback) by transmitting HARQ ACK on PUCCH according to the current RRMconfiguration and/or virtual cell configuration (e.g., in subframe n+4).Reception of such control signaling by the WTRU (e.g., with aconfiguration index) may activate the corresponding RRM configurationand/or virtual cell configuration (e.g., and/or RRM parameters thereof).The WTRU may resume decoding of the PDCCH and/or ePDCCH after a giventime (e.g., fixed and/or signaled) from the reception of the concernedsignaling (e.g., at subframe n+4, subframe n+15, etc.). In an example,activation/deactivation of a virtual cell may be used as a groupingmethod.

From the perspective of the network, the SCeNB may provide a number ofconfiguration values for one or more RRM configurations and/or virtualcell configurations to the MeNB. The SCeNB may indicate the indexingmethod to be used. For example, such configuration may be forwarded onthe interface between the SCeNB and the MeNB (e.g., a modified X2 suchas the X2bis). The SCeNB may prepare the RRC Connection ReconfigurationMessage with the RRM configuration(s) and/or virtual cellconfiguration(s) and send the RRC Connection Reconfiguration Message tothe MeNB to be forwarded to the WTRU. The scheduler in the MAC instanceassociated with the for the secondary layer may then use L1 signalingand/or L2 signaling to dynamically switch between configuration valuesfor one or more RRM aspects.

When a WTRU is configured to operate utilizing multiple layers orserving sites that are associated with different schedulers, a radiobearer may be associated exclusively with a single MAC instance and/or aplurality of MAC instances. One or more serving cells associated with agiven layer/MAC instance may fail, for example due to poor radio linkconditions, reconfiguration failure, mobility failure, radio linkfailure, and/or for other reason(s). Additionally, a WTRU configuredwith one or more serving cells associated with a given layer/MACinstance may be handed over to a different set of serving cell(s) thatmay be associated with a different network entity (e.g., logical entitysuch as a cell or physical entity such as an eNB). Methods are describedto address the loss of radio link across one or more serving sites/MACinstances and/or to address mobility on a serving site specific basis(e.g., applied to a set of serving cells associated with a specificlayer/MAC instance). Methods and systems are disclosed for efficientmanagement of MAC instances to ensure service continuity during mobilityevents. For example, methods and systems are described for performingmobility events when one or more radio bearers (e.g., SRBs and/or DRBs)are associated with a layer/MAC for which a mobility event is beingperformed.

As an example, a WTRU may establish a connection to a first eNB. Forexample, the first eNB may be a MeNB. The connection to the first eNBmay be considered a primary layer and/or the first eNB may be considereda first serving site and/or primary serving site. As part of the WTRUcapability exchange during the initial RRC connection procedure with thefirst serving site, the WTRU may provide a first set of WTRUcapabilities, for example in order to establish a connection to thefirst serving site according to Release 11 connectivity procedures.Additionally, as part of the initial connection procedure to the firstsite, the WTRU may provide a second set of WTRU capabilities, and thesecond set of WTRU capabilities may be associated with connectivityinformation supported by the WTRU for establishing connectivity to asecond layer or serving site. The MeNB and another eNB (e.g., a SCeNB)may subsequently coordinate to configure of the WTRU to access multipleserving sites according to the respective capabilities, for exampleusing multiple MAC instances.

In an example, when establishing a connection to a first eNB (e.g., aMeNB associated with a primary layer/first serving site) the WTRU mayinclude an indication of whether or not the WTRU supports dualconnectivity, for example as part of the WTRU capability information. Ifthe WTRU indicates dual connectivity is supported, the WTRU may includeassociated WTRU capabilities for accessing a secondary serving site whenestablishing the connection with the first serving site. Uponsuccessfully connecting to the first serving site, the WTRU may, forexample when initially establishing connectivity to a SCeNB, provide asecond set of WTRU capabilities to the SCeNB. The MeNB and the SCeNB maysubsequently configure the connection of for the WTRU for each of theserving sites using their respective parameters according to thecapability information provided by the WTRU.

After establishing a connection to a primary serving site (e.g., an RRCconnection) for example using Release 11 procedures, the initialconfiguration of a secondary layer may be in a variety of manners. Forexample, a WTRU that is connected to a first eNB (e.g., a MeNB, aprimary layer, a first serving site, a connection via a first MACinstance, etc.) may be configured to operate with one or more cells froma second eNB (e.g., an SCeNB, a secondary layer, a second serving site,a connection via a second MAC instance, etc.). For example, the WTRU mayreceive control plane signaling (e.g., RRC signaling) such that a secondset of cells may be configured to form a secondary layer for the WTRUconfiguration. The configuration of the secondary layer may be performedusing RRC signaling received using dedicated resources and/or dedicatedRRC messages.

As an example, the initial configuration of the secondary serving siteconnection may be performed using a reconfiguration procedure. The WTRUmay perform a reconfiguration procedure with the primary layer, and thereconfiguration procedure may be used to establish connectivity to thesecondary serving site. Thus, signaling form the primary serving sitemay be used to configure the WTRU to operate using the secondary layer.The signaling configuring the secondary layer may be received viaresources of a primary layer, for example if an RRC connectionassociated with the primary layer is used to configure a secondarylayer. An RRC Connection Reconfiguration procedure may be used. Forexample, the WTRU may perform an RRC connection reconfigurationprocedure with the primary serving site that configures the WTRU tooperate using the secondary serving site.

The initial configuration of the secondary serving cell may be a type ofa mobility event. For example, after establishing an RRC connection witha primary serving site, resources associated with the primary servingsite may be used to perform a mobility procedure. During the mobilityprocedure the WTRU may maintains its configuration, connectivity, and/oroperational status with the primary serving site, but may add one ormore serving cells of a secondary layer to its configuration. Forexample, an RRC Connection Reconfiguration procedure may be performed,for where the mobility control information element is transmitted to theWTRU (e.g., a handover command may be sent to the WTRU). Rather than theWTRU interpreting the handover command to mean that the WTRU shouldperform a handover from a cell of the primary serving site to some othercell, the handover command may configure one or more cells of asecondary serving site to be used in addition to cells of the primaryserving site. The handover command may include an indication that thehandover command is to establish dual connectivity rather than totrigger handover of the WTRU from a cell of the primary serving site.The mobility related signaling received on resources of the primarylayer may configure a Primary Cell (PCell) in the secondary layer at atarget eNB (e.g., the SCeNB). After establishing the connection with thePCell of the secondary layer, the WTRU may receive a RRC ConnectionReconfiguration message from the target eNB (e.g., the SCeNB) that addsadditional serving cells such as SCells associated with of the secondaryserving site.

The initial configuration of the secondary layer/serving site (e.g., asa reconfiguration of the primary serving site and/or a mobility event atthe primary serving site) may include a radio bearer reassignment. Forexample, when performing a connection reconfiguration procedure and/ormobility procedure with the primary serving site in order to establishconnectivity to the secondary serving site, one or more existing radiobearers (e.g., radio bearers previously associated with primary servingsite transmission) may be moved to the secondary layer/serving site. Theradio bearers may be move exclusively to the secondary serving siteand/or may be moved such that they are associated with both the primaryserving site and the secondary serving site.

Addition of a secondary layer may be performed once security isactivated for the primary layer. For example, in order to add a PCell ofa secondary serving site, the WTRU may wait until the security contextassociated with the WTRU connection to the primary serving site has beenactivated. For example, configuration of a secondary serving site may beperformed once Access Stratum (AS) security has been activated and/oronce SRB2 with at least one DRB have been established/setup (e.g., andare not suspended) for the connection associated with the first eNB(e.g., the primary layer).

In an example, a common security context may be utilized across aplurality of serving sites, and bearer identities may be WTRU-specific.If the secondary layer implements a security context that is common withthat of the primary layer or some other active serving site (e.g., forone or more of the control plane and/or for the user plane), theconfiguration of the secondary layer may be performed using a commonidentity space for the bearer identification (e.g., srb-Identity and/ordrb-Identity). For example, if one or more serving sites utilize thesame bearer identification(s), the transmission scheme may beestablished such that none of the bearer identities that are utilizedare used in multiple layers/serving sites with different PDCP entities.By doing so the WTRU can avoid the scenario where different PDCP PDUsare transmitted using the same security keys and the same sequencenumber (e.g., such a scenario may lead to processing/identificationdifficulties at the PDCP layer in the WTRU).

In an example, separate security contexts may be utilized for differentserving sites, and bearer identities may be layer-specific. For example,if separate security contexts are utilized accords the layers, areconfiguration procedure (e.g., used to initially configure thesecondary layer) may be performed while security is not active atsecondary layer. If the secondary layer implements a separate securitycontext (e.g., for one or more of the control plane and/or the userplane), configuration of the secondary layer may be performed whensecurity has either not yet been started/activated (e.g., for an initialconfiguration of the secondary layer) and/or has failed (e.g., for areconfiguration that moves one or more RBs to another layer). Alayer-specific security mode command may be used to activate security ata secondary layer. For example, the security activation procedure may beperformed and/or the security mode command may be sent for a given layerwhenever the layer-specific Kenb is changed and/or when the NAS COUNT ischanged.

Depending on the current load in the network and/or the amount of datato be transmitted to and/or from a WTRU, the WTRU may be configured witha primary layer and zero or more secondary layer(s). The WTRU may beconfigured with measurement information on a layer-specific basis and/orwith cell-specific offsets in order to define a region of a cell. A WTRUmay be configured with a measurement object (e.g., measObj). Thismeasurement object may be cell-specific and/or layer-specific. Themeasurement object may be associated with one or more other eventconfigurations (e.g., eventConfiguration), for example depending on theWTRU configuration. An event configuration may include one or morecriterion that trigger one or more WTRU behaviors. For example, withrespect to the measurement object, the WTRU may be configured with oneor more event configurations (e.g., criteria) that establish conditionsunder which the WTRU is triggered to perform an action based on the WTRUmeasurements related to the measurement object. As an example, themeasurement object may establish a measurement for a serving cell of theprimary and/or secondary serving site, and the event configurations mayindicate one or more thresholds and/or an offset amounts associated withthe measurement object. If the concerned measurement is above aconfigured threshold, below a configured threshold, exceeds a givenoffset value, etc., the WTRU may be triggered to perform an eventassociated with the event configuration. The initial configuration of asecondary cell may include one or more associations between measurementobjects for a cell of the secondary serving site and one or more eventconfigurations that establish actions that the WTRU is to perform in theprimary and/or secondary layer if the measurement meets specifiedcriteria. The measurement object may be associated with one or moreevent configurations using a measurement identity (measId) that is usedby the network to refer to a given measurement object or configuration.

For example, a measurement object for a given layer may be configuredfor a given serving cell of the layer. The even configurations mayestablish actions to be performed by the WTRU based on the quality ofthe serving cell becoming better than a first threshold (e.g., acondition that may trigger a first behavior), based on the quality ofthe serving cell becoming worse than a second threshold (e.g., acondition that may end the first behavior and/or that may trigger asecond behavior), etc. One or more measurement objects and one or moreevent configurations may be used to define a cell range expansion (CRE)region. A CRE region may be established with respect to a macro cell(e.g., associated with a MeNB) and one or more small cells (e.g.,associated with one or more SCeNBs). The CRE region of the MeNB may beassociated with regions where the WTRU is with the coverage area of theMeNB and is also within the coverage of one or more small cells of theSCeNBs. While the WTRU is within the CRE, traffic from the macro cellmay by offloaded to one or more of the small cells. The CRE may bedefined based on measurements of cells in one or more layers. The WTRUmay be configured to determine whether it is within a CRE based on themeasurements of one or more small cells (e.g., whether serving cellquality is above a threshold, below a threshold, etc.) while it is stillconnected to the macro cell. WTRU behavior may be defined based on oneor more of whether the WTRU is within coverage of the CRE region,whether the WTRU detects entering the CRE region (e.g., either from ortowards the cell center), whether the WTRU detects leaving the CREregion (e.g., either from or towards the cell center), and/or the like.

Conditions detected at a first cell associated with a first serving siteor layer may trigger certain WTRU behavior in a secondary serving siteor layer. For example, if a neighbor cell in a different layer becomesbetter than a serving cell of a current layer (e.g., by a specifiedoffset), the WTRU may be triggered to perform a first function and/orstop performing a second function. Similarly, if a neighbor cell in adifferent layer becomes worse than a serving cell of a current layer(e.g., by a specified offset), the WTRU may be triggered to perform asecond function and/or to stop performing the first function.

The WTRU may be configured with one or more offset values (e.g., valuesby which a neighbor cell may be above or below a value of the currentserving cell in order to trigger a behavior) and/or one or more absolutethreshold values (e.g., specific levels at which a measurement triggersa given behavior). In terms of multi-layer operation, if certaincriteria related to measurements performed on a cell associated with theprimary layer and/or a cell associated with a secondary layer are met,the WTRU may perform one or more actions related to a specific layer(e.g., initiate decoding of control signaling in another cell/layer,activate a cell/layer, etc.). Thus, instead of (and/or in addition to)legacy measurement reporting triggers, a given measurement may triggerother behavior in other layers. For example, a WTRU configured with dualconnectivity may be configured with a measurement in a first layer andmay be triggered to perform actions related to the serving cell of asecondary layer (e.g., a measurement of a cell in the secondary layer)based on certain criteria regarding the measurement in the primary layerbeing met. For example, measurement criteria may be established toindicate that the WTRU is within the CRE region but that the quality ofa secondary cell is decreasing (e.g., indicating that the WTRU is movingtowards the edge of the small cell). Such measurement criteria may beused to trigger the WTRU to send a request for re-establishment of atleast one bearer configured for use in the secondary layer.

In an example, the WTRU may be configured to attempt to determinewhether it is within a CRE region but that the quality of the cellassociated with the secondary layer is decreasing. For example,measurements may be configured such that if the WTRU detects that thequality of the secondary serving cell is falling below a threshold butis still within the CRE region (e.g., indicating that the WTRU movingtowards the edge of the cell), the WTRU may be triggered to beginreception of control signaling in a different cell. For example, thedifferent cell may be associated with a different SCeNB for which theWTRU has been preconfigured, but that had not been activated in theWTRU. The WTRU may begin attempting to receive the control signaling(e.g., RRC signaling) in the other cell in order to attempt to maintainsession continuity during the activation/deactivation of differentlayer. For example, measurements may indicate that the WTRU is movingtowards the edge of a small cell, and the WTRU may be triggered toinitiate reception of control signaling in a macro cell. Since the macrocell may have a larger coverage area than the small cells, the WTRU maybe more likely to receive the control signaling via the macro cell whenmoving to a cell edge of the small cell. The initiation of reception ofcontrol signaling in the macro cell may be performed in addition toand/or or after transmission of a measurement report to the network(e.g., through the current serving cell of the small cell layer).

Reconfiguration procedures may be utilized in order to configure one ormore secondary cells for use. For example, an RRC connectionreconfiguration procedure may be utilized by the WTRU to configure asecondary layer using control signaling exchanged with the primarylayer. The configuration of the second set of cells that are associatedwith a secondary serving sit and/or secondary MAC instance (e.g.,referred to as a secondary layer) may be performed as part of the RRCconnection reconfiguration procedure. For example, the control signalingused to establish a configuration for one or more cells in a secondarylayer may include an RRC Connection Reconfiguration message without themobilityControlInfo information element (e.g., received via a cell ofthe primary layer). For example, the WTRU may receive anRRCConnectionReconfiguration message, for example via a transmissionfrom a cell associated with the primary layer and/or over an SRBassociated with the primary layer (e.g., in case of initialconfiguration for the small cell layer). In an example, if the secondarylayer has already been established, the RRCConnectionReconfigurationmessage may be received on a transmission from a cell associated with asecondary layer and/or over an SRB associated with a secondary layer(e.g., reconfiguration of PHY/MAC parameters for the secondary layer;for addition, removal, re-association and/or moving of one or more RBsfrom one layer to the other, etc.).

In an example, rather than reusing the RRCConnectionReconfigurationmessage for configuring a secondary layer, a new RRC message may beestablished for configuring a MAC instance associated with a secondarylayer. For example, an RRCConnectionReconfigurationSecondaryLayermessage may be defined for initially configuring and/or reconfiguring asecondary layer. If an RRCConnectionReconfiguration message is utilized,an indication may be included in the message that indicates that thereconfiguration is being performed in order to configure/reconfigure asecondary layer rather than or in addition to a primary layer. Theconfiguration information for the secondary layer may be applicable to asecond group of cells served by a serving site associated with thesecondary layer (e.g., a SCeNB). The cells secondary layer may bescheduled independently of cells of other layers. The configuration forthe secondary layer may include configuration information for a PCelland zero or more SCell(s). In an example, the cells of a given layer maybe associated with the same Timing Advance Group.

Whether the reconfiguration message is used to initially configure thesecondary layer and/or reconfigure the secondary layer, thereconfiguration message may include a one or more parameters that theWTRU may apply for operation in the secondary layer (e.g., theparameters may be in addition to existing parameters of such RRCmessage). For example, an RRCConnectionReconfiguration message used forconfiguring/reconfiguring a secondary layer may include a dedicatedradio resource configuration for one or more serving cell(s) of thesecondary layer (e.g., a radioResourceConfigDedicated IE for a cell ofthe secondary serving site). For example, the dedicated radio resourceconfiguration may be for a PCell of the secondary layer. In an example,an RRCConnectionReconfiguration message used forconfiguring/reconfiguring a secondary layer may include an indicationand/or a list of one or more secondary layers to be added (an/or to bemodified (e.g., a sLayerCellToAddModList IE which may identify layersbeing added). In an example, an RRCConnectionReconfiguration messageused for configuring/reconfiguring a secondary layer may include a listof one or more serving cell(s) to add (and/or to modify) correspondingto cell(s) of a secondary layer (e.g., a pCellToAddModList thatindicates information for PCell(s) to add/modify and/orsCellToAddModList that indicates information for SCell(s) toadd/modify). For example, for each layer indicated (e.g., via thesLayerCellToAddModList IE), a list of cells to add may be provided(e.g., via a pCellToAddModList and/or sCellToAddModList).

In an example, an RRCConnectionReconfiguration message used forconfiguring/reconfiguring a secondary layer may include one or moreparameters for security key derivation. For example, the reconfigurationmessage may indicate whether new security keys are to be derived for usewith a secondary layer and/or an indication of the method to be used toderive the security key. In an example, an RRCConnectionReconfigurationmessage used for configuring/reconfiguring a secondary layer may includean indication of a layer identity (e.g., a layer-identity IE,mac-instanceIdentity IE, etc.). The layer identity may be used forderiving identities for one or more SRBs of the secondary layer (e.g.,for purpose of security input such as a BEARER parameter). For example,for a given SRB, the value provided by RRC to lower layers to derive the5-bit BEARER parameter used as input for ciphering and for integrityprotection may be the value of the correspondingsrb-Identity+2*layer-identity, for example with the MSBs padded withzeroes. As an example, the primary layer may be allocated the identity0. The identity of secondary layer may be implicitly derived based onthe configuration sequence. In an example, anRRCConnectionReconfiguration message used for configuring/reconfiguringa secondary layer may include an indication of one or more associatedRBs (e.g., one or more DRB(s) and/or SRB(s)) that are being associatedwith the secondary layer. If bearers may be split across differentlayers, the RRCConnectionReconfiguration message used forconfiguring/reconfiguring a secondary layer may include a service accesspoint identity associated with a secondary layer (e.g., such anindication may also be provided even if the bearers are specific to agiven layer).

Upon reception of the RRCConnectionReconfiguration message, the WTRU mayperform various functions, for example based on the contents of thereconfiguration message. For example, the WTRU may add a first cell fora secondary layer, add an additional cell to a secondary layer, remove acell from a secondary layer, etc. As an example, if the reconfigurationmessage indicates the addition of one or more secondary layers and/orone or more cells of a secondary layer, the WTRU may perform an initialconfiguration of a cell for a secondary layer. As an example if the cellto be added is the first cell being configured and added for a givensecondary layer, the WTRU may create a secondary MAC instance, forexample using a mac-MainConfig IE provided in theradioResourceConfigDedicated IE that may be included in thereconfiguration message. The WTRU may associate the newly createdsecondary MAC instance with an identity. For example, an explicitindication of the identity may be provided in the reconfigurationmessage and/or may be implicitly created based on incrementing a counterof the instantiated (e.g., configured) MAC instances. The WTRU mayconfigure a physical layer (e.g. possibly using a separate transceiverchain) associated with the secondary MAC instance. For example,parameters for the physical layer may be include in theradioResourceConfigDedicated IE included in the configuration applicableto the MAC instance (e.g., physicalConfigDedicated). The WTRU mayimplicitly consider the first cell configured for use in the newlycreated layer to be a PCell for the secondary layer. The WTRU maysynchronize to the downlink of the configured cell for the newly addedlayer (e.g., if the cell is configured as a PCell of the concernedlayer). If the cell being added is not the first cell being configuredfor the secondary layer, the WTRU may apply any configurations receivedfor the cell to the existing MAC instance, and may refrain from creatinga new MAC instance.

The reconfiguration message may be used to remove or delete a cell froma secondary layer. For example, if the reconfiguration indicates that acell should be removed, the WTRU may remove the indicated cell(s) andupdate the MAC instance configuration. If a secondary MAC instance isconfigured with zero cells following the completion of the processing ofthe reconfiguration message (e.g., each of the cells for the layer havebeen removed), the WTRU may remove the corresponding secondary MACinstance from its configuration.

In an example, the use of the RRC connection reconfiguration messagewithout the mobilityControlInfo IE may be associated with modifying anexisting connection for a secondary layer, but not for adding a newlayer (e.g., the use of the reconfiguration message without themobilityControlInfo IE occurs when the WTRU is already configured fordual connectivity and one or more secondary layers are being modified).For example, if the WTRU has not previously received an initialconfiguration for a secondary layer in a RRC connection reconfigurationmessage that includes the mobilityControlInfo IE, the WTRU may determineto discard the RRC configuration included in a reconfiguration messagewithout the mobilityControlInfo IE that is applicable to a layer thatwas not previously configured.

For example, the configuration of a secondary layer may be establishedbased on an RRC Connection reconfiguration procedure that includes themobilityControlInfo IE. The configuration of the second set of cellsand/or secondary MAC instance (e.g., the secondary layer) may beperformed as part of the RRC connection reconfiguration procedure. TheRRC connection reconfiguration message including the mobilityControlInfoinformation element may be referred to as a handover command. If ahandover command is the type of signaling used to add a secondary layer(e.g., and a an RRC connection reconfiguration message without themobilityControlInfo IE is used to modify existing layer configurations),then the WTRU may perform one or more of the actions described hereinfor adding a new layer upon receipt of the handover command (e.g.,addition of PCell to the new layer, creation of secondary MAC instance,associate the secondary MAC instance with an identity, configure thephysical layer, synchronize to a PCell of the new layer, etc.).Additionally, if a handover command is the type of signaling used to adda secondary layer (e.g., and a an RRC connection reconfiguration messagewithout the mobilityControlInfo IE is used to modify existing layerconfigurations), then the handover command may include one or more ofthe configuration parameters described herein for adding a new layer(e.g., a dedicated radio resource configuration for a cell of the newlayer, a list of one or more layers to add, a list of one or moreserving cells for the layer, a parameter for security key derivation, alayer identity, an indication of associated RBs, etc.).

The WTRU may receive an indication that the reconfiguration procedureincluding the handover command is for addition of a layer. The WTRU maymaintain its configuration information for the currently configuredserving cells if the handover command is adding a new layer. Theindication that the handover command is being used to add a layer mayexplicitly indicate which other layers the WTRU should maintain itscurrent configuration for.

If the WTRU fails to reconfigure a primary layer during areconfiguration procedure, the WTRU may release and clear anyconfiguration corresponding to both the primary layer and one or moresecondary layers. The WTRU may perform reconfiguration failure handlingas per legacy procedures, for example, by reselecting to a differentcell, initiating a reestablishment procedure, moving to IDLE mode,and/or the like.

Upon successfully completing the RRC procedure that is used to initiallyconfigure the secondary layer and/or upon successfully completing theRRC procedure that reconfigures one or more secondary layers, the WTRUmay autonomously trigger RACH reconfiguration, may monitor for a RACHorder after the reconfiguration and after an activation time, and/oractivate one or more cells via RACH.

For example, the WTRU may be configured to autonomously trigger RACHreconfiguration upon successfully adding and/or reconfiguring asecondary layer. The WTRU may initiate a RACH procedure for thesecondary layer. In an example, the UE may receive an indication in thereconfiguration message for the layer that a RACH procedure should beperformed. In an example, the RACH procedure may be performed if theWTRU receives the reconfiguration message configuring the new layerusing resources of the primary layer (e.g., from MeNB), but not if thereconfiguration is performed via the secondary layer. The RACH proceduremay be performed using a dedicated PRACH configuration provided in thereconfiguration procedure (e.g., in the handover command or otherreconfiguration message). In an example, the presence of a PRACHconfiguration in the reconfiguration message may be an indication thatthe WTRU is to initiate the RACH procedure upon completion of thereconfiguration procedure. The RACH procedure may be performed usinguplink resources of a serving cell of the newly added or reconfiguredsecondary layer. The RACH procedure may be performed via a PCell of thesecondary layer. The RACH procedure may be performed on an SCell of thesecondary layer. Which cell of the newly added/reconfigured layer shouldbe used for the RACH procedure may be indicated in the reconfigurationmessage. The TAT associated with the serving cell on which the RACHprocedure is to be performed may be considered to be stopped or notrunning following the reconfiguration procedure.

In an example, the WTRU may monitor for a RACH order after thereconfiguration procedure and/or after an activation time for thesecondary layer. For example, the WTRU may begin monitoring for a RACHorder on a PDCCH for a serving cell of the secondary layer upon thecompletion of the reconfiguration procedure adding and/or modifying asecondary layer. The WTRU may begin monitoring the PDCCH after aconfigured and/or predefined activation time. The serving cell to bemonitored for the RACH order may be a PCell of the newlycreated/reconfigured secondary layer and/or may be a SCell of the newlycreated/reconfigured secondary layer. Which cell of the newlyadded/reconfigured layer should be monitored for the RACH order may beindicated in the reconfiguration message. The TAT associated with theserving cell on which the RACH procedure is to be performed (e.g., overwhich the RACH order is received) may be considered to be stopped or notrunning following the reconfiguration procedure.

In an example, the cells of a newly created/reconfigured layer may beconsidered to be initially deactivated. Upon activation of the layer,the WTRU may be configured to perform a RACH procedure on a cell of thelayer being activated. For example, the WTRU may determine to associatea deactivated state to each of the cells of a newly added/reconfiguredlayer. In an example, the Scells of the layer may be initiallydeactivated, but the PCell of the layer may be consider activated uponreceiving the configuration for the layer. Reception of controlsignaling that activates a cell of a newly added/reconfigured layer maytrigger the WTRU to perform a RACH procedure and/or begin PDCCHmonitoring of a cell of the newly added/reconfigured layer. For example,the reception of control signaling (e.g., from the MeNB) that activatesone or more cell(s) of a secondary layer (e.g. that is received whileall cell(s) of the secondary layer are in deactivated state) may triggerthe WTRU to perform a RACH procedure and/or begin monitoring the PDCCHfor a cell of the layer being activated.

The WTRU may be configured to transmit and/or receive RRC signaling fromindependent eNBs and/or independent RRC entities within the network. Forexample, according to LTE Release 11 procedures, when an RRC procedureis initiated, the WTRU may be allowed as maximum time allowed tocomplete the RRC procedure. For example, typical values for the maximumamount of time the WTRU may take to complete the RRC procedure may be inthe range of 15 ms to 20 ms, depending on the RRC procedure. RRC alsosupports back-to-back reception of RRC messages, for example when an RRCmessage that initiates a second procedure is received while a first RRCprocedure is ongoing and not yet completed. In such a case, the WTRU mayprocess the RRC messages sequentially. When the WTRU has connectivity toa single eNB, the network may ensure proper coordination of the RRCsignaling such that WTRU processing and timing requirements areminimized.

When the same eNB sends both messages, the eNB may be able to determinethe total delay for the combination of RRC procedures. The delay may bedetermined independently of how many RRC messages the eNB sends to theWTRU. In this scenario there may be no timing uncertainty at the eNB andsynchronization may be entirely controlled by the eNB.

When dual connectivity is configured (e.g., the WTRU is connected toand/or attempting to connect to multiple layers), there may conflicts incases where eNBs are not entirely coordinated. For example, the WTRU mayreceive control signaling from multiple eNBs that each initiate arespective RRC procedure. The received control signaling may be sentover different transmission paths (e.g., the Uu of the MeNB and the Uuof the SCeNB). For example, the path utilized for sending the RRCmessages may depend on whether the signaling is applicable to the WTRUconfiguration for the MeNB or for the SCeNB. In such a case, there is ahigher probability that the WTRU may receive a RRC message that triggersa second RRC procedure (e.g., with the SCeNB) while the WTRU already hasan ongoing RRC procedure (e.g., with the MeNB) (or vice-versa).

When the WTRU receives RRC messages from different eNBs (e.g., a SCeNBand a MeNB) it may be challenging for a second eNB to ensuresynchronization and the completion of the procedure with the WTRU. Forexample, it may be difficulty to determine the delay before thecompletion of the procedure, as the WTRU may already be performinganother RRC procedure initiated by a first eNB. The second eNB may beunaware of the other RRC procedure that the WTRU is performing. Inaddition, it may be difficult for a WTRU to perform RRC procedures inparallel (e.g., instead of sequentially), for example if there is adependency (or interaction) between the two RRC procedures. For example,issues may arise in one or more of the conflicting procedures, regardingsynchronization, timing uncertainty, additional delay, etc.

For example, there may be colliding RRC PDU reception by the WTRU forthe different RRC procedures. In an example, the WTRU may be configuredto prioritize one or the RRC procedures that may be associated with afirst layer over another RRC procedure that may be associated with asecond layer. For example, the WTRU may handle the reception of aplurality of RRC PDUs in the same subframe (or within processing windowsthat may overlap) by associating a priority to each message. Thepriority may be assigned according to predefined rules, for example suchthat the WTRU may sequentially perform the associated procedures inorder of increasing priority. For example, the priority assigned to agiven RRC procedure and/or a given RRC message may be based on theidentity of the layer that the RRC PDU is associated with (e.g., theprimary layer/MeNB may have higher priority than a secondarylayer/SCeNB), the identity of the SRB that the WTRU receives the RRC PDUover (e.g., SRB0, SRB1, SRB2 may have higher priority than SRB3), thetype of procedure the RRC PDU is associated with (e.g., a mobility eventsuch as a handover command may have a higher priority than areconfiguration procedure), and/or the like.

In an example, in the case of colliding RRC PDU reception, the WTRU maybe configured to prioritize an RRC PDU that synchronizes based on adelay requirement. For example, the WTRU may assign a lower priority toa RRC PDU associated with a procedure whose completion may trigger aRACH procedure. The timing of the procedure with higher priority may bemaintained, while the second procedure may still be performed withoutintroducing timing uncertainty given that the RACH procedure that isperformed after completion of the lower priority RRC procedure maysynchronize the WTRU and the network.

In an example, upon reception of an RRC PDU while another RRC procedureis ongoing, the WTRU may be configured to prioritize one of theprocedures and suspend/abort the other RRC procedure. For example, theWTRU may suspend or abort an ongoing procedure based on receiving an RRCmessage that is determined to be of a higher priority. For example, theWTRU may determine that two received RRC PDUs and/or an ongoingprocedure and a received RRC PDU conflict, in which case the WTRU mayinitiate RRC procedure failure logic for the RRC PDU and/or procedurewith lowest priority. In an example, the WTRU may suspend a procedurewhose completion may result in a RACH procedure in the case of such aconflict.

For example, two or more RRC PDUs may be received concurrently or nearlyconcurrently. As an example, the WTRU may receive multiple RRC PDU(s) inthe same subframe and/or within a certain amount of time. A first RRCPDU may be associated with a procedure applicable to a first eNB/layerand a second RRC PDU may be associated with a procedure applicable to asecond eNB/layer. In the case of such a conflict, the WTRU may performparallel processing of the RRC procedures, sequential processing of theRRC procedures, and/or may drop or perform a failure procedure for oneor more of the RRC procedures.

For example, the WTRU may process both messages such that RRC proceduresmay be performed in parallel. For example, the WTRU may determine toperform the RRC procedures in parallel if the RRC procedures areindependent from each other. For example, the WTRU may determine thatboth procedures reconfigure different RRC aspects (e.g., differentparameters, different RBs, different MAC instances, differenttransceiver components, and/or independent combinations thereof) andthat the reconfigurations are not conflicting with each other. The WTRUmay perform the RRC procedures in parallel based on determining thatboth procedures are independent in nature (e.g. a measurementconfiguration and a reconfiguration of dedicated resources). Forexample, the WTRU may determine that the processing requirement (e.g.,in terms of maximum delay) to complete the procedure(s) are the same asfor the case where each procedure would have been performed separately.Otherwise, the WTRU may be configured to perform synchronization withthe network (e.g., by performing a RACH procedure). For example, iftiming uncertainty is introduced for both the MeNB and SCeNB for an RRCprocedure due to the configuration of dual connectivity, the WTRU may beconfigured to perform a RACH procedure for one or more RRC proceduresthat modify the corresponding physical layer parameters of the WTRUand/or for each of the reconfigured physical layers.

In an example, the WTRU may be configured to perform sequentialprocessing of two or more RRC procedures. The WTRU may process thereceived messages in sequence, such that RRC procedures are performedsequentially. For example, the WTRU may determine to perform the RRCprocedures sequentially based on determining that both RRC proceduresare independent from each other. The WTRU may determine which procedureto prioritize (e.g., to perform first) based on one or more of theidentity of the eNB associated with the RRC procedure, an identity ofthe SRB associated with the RRC procedure, the type of RRC PDU that isreceived, the type of RRC procedure, and/or the like.

For example, the WTRU may determine which RRC procedure toprioritize/perform first as a function of the identity of eNB (and/orlayer/Uu interface) associated with the RRC procedure. For example, theWTRU may prioritize the processing of a RRC PDU associated with a MeNBover that of an SCeNB.

For example, the WTRU may determine which RRC procedure toprioritize/perform first as a function of the identity of the SRBassociated with the procedure. For example, the WTRU may determine thatthe SRB over which the RRC PDU is received is the same or different asthat of the RRC PDU that initiated an ongoing procedure. In an example,if the set of SRB(s) used for a first eNB and for a second eNB aredifferent, than certain SRBs may be prioritized over other SRBs. Forexample, if the SRBs for a given WTRU shared the same identity spaceacross the different layers/MAC instances, then the WTRU may determinewhich procedure to prioritize directly based on the identity of the SRBsfor the procedures. Otherwise, if the SRBs for a first layer aredifferent than that of a second layer, then the WTRU may determine whichRRC procedure to prioritize based on association(s) between an SRBidentity and an eNB (e.g., the WTRU may have SRB0, 1, and/or 2 for eacheNB and the priority may be based first on the SRB identity and in caseof the same SRB identity based on the layer identity). For example, theWTRU may prioritize the processing of a RRC PDU associated with SRB0,SRB1, and/or SRB2 over a RRC PDU associated with SRB3.

The WTRU may determine which RRC procedure to prioritize/perform firstas a function of the multiplexing method used for reception of RRC PDUsassociated with the WTRU configuration for different eNBs. For example,the WTRU may determine the priority associated with a given RRCprocedure based on the function that enables multiplexing of RRC PDUs(or information elements in the PDU) pertaining to the configuration fordifferent eNBs. For example, the identity of the Uu interface that wasused for the transport of the RRC PDU may be used to establish apriority. The RRC PDU format (e.g., such as an indication received inthe RRC PDU and/or the type of information element(s) included in theRRC PDU) may be used to establish an RRC priority. The identity of thesubframe in which the WTRU received an RRC PDU may be used to determinea priority for handling RRC procedures (e.g., in case the downlink ofthe WTRU is time-multiplexed between the eNBs).

The WTRU may determine which RRC procedure to prioritize/perform firstas a function of the type of RRC PDU received. For example, the WTRU maydetermine the priority associated with a given RRC PDU as a function ofwhether the RRC PDU initiates a new RRC procedure or is a PDU for anongoing procedure. The WTRU may be configured to prioritize an RRC PDUfor an ongoing procedure over an RRC PDU that initiates a new RRCprocedure. In an example, if RRC PDUs applicable to WTRU configurationsfor either eNB/layer may be received on either of the transport paths(e.g., RRC PDUs for RC procedures associated with different layers maybe received on the same transport path), then ongoing procedures may beprioritized over newly initiated procedures. For example, the WTRU mayprioritize a RRC PDU associated with an ongoing procedure over a RRC PDUthat initiates a new procedure.

The WTRU may determine which RRC procedure to prioritize/perform firstas a function of the type of procedure associated with the received RRCPDU(s). For example, the WTRU may determine the priority associated witha RRC PDU based on the type of RRC procedure that the RRC PDU isassociated with. For example, a WTRU may prioritize a RRC PDU associatedwith a mobility event or to a security event over an RRC PDU associatedwith a reconfiguration of a secondary layer.

The WTRU may be configured to drop and/or initiate a failure procedurefor an RRC procedure that conflicts with another RRC procedure of higherpriority. For example, the WTRU may determine that a second RRC PDUshould be ignored and/or that the WTRU should proceed to failure logicfor an RRC procedure associated with the second RRC PDU based ondetermining that another RRC procedure invalidates and/or conflicts withthe RRC procedure associated with the second RRC PDU and that the otherRRC procedure has a higher priority than the RRC procedure associatedwith the second RRC PDU. For example, the WTRU may drop an RRC PDU orinitiate failure logical for an RRC procedure associated with the RRCPDU based on determining that the procedures are dependent on eachother. For example, the WTRU may receive an RRC reconfiguration messagewith the mobilityControlInfo IE (e.g., a handover command) thatinstructs the WTRU to remove the configuration associated with an SCeNBand to perform a handover to another cell for the RRC Connection. TheWTRU may also receive an RRC reconfiguration message that is meant toreconfigure the SCeNB (e.g., such as the physical layer configuration ofthe SCeNB). In such a case, the WTRU may process and perform themobility procedure (e.g., associated with the handover command) anddetermine that the reconfiguration procedure for the SCeNB is invalid.In an example, the WTRU may transmit a message indicating the failure toperform the second procedure, and the message may include an indicationof the cause of the failure (e.g., “override by MeNB”).

A similar priority based rules may be applicable in the WTRU forWTRU-initiated RRC procedures. For example, when the WTRU determinesthat more than one RRC procedures should be triggered within a certainpredetermined period of time, the WTRU may utilize the priority rulesfor determining how to handle conflicts for the two or more WTRUinitiated RRC procedures.

In an example, a WTRU may be configured to receive one or more RRCPDU(s) for an RRC procedure while another RRC procedure is ongoing. Forexample, the ongoing RRC procedure may be applicable to a firsteNB/layer and the received RRC PDU(s) may be associated with a procedureapplicable to a second eNB/layer. In such a case, similar rules may bedefined performing parallel processing of the RRC procedures, sequentialprocessing of the RRC procedures, and/or dropping or performing afailure procedure for one or more of the RRC procedures as was the casewhen two or more RRC PDUs are received concurrently or nearconcurrently.

For example, the WTRU may process the received RRC PDU applicable to aconfiguration for the second eNB/layer such that the second RRCprocedure is performed in parallel to the ongoing RRC procedure. Forexample, the WTRU may determine to perform the RRC procedures inparallel if the RRC procedures are independent from each other. Forexample, the WTRU may determine that both procedures reconfiguredifferent RRC aspects (e.g., different parameters, different RBs,different MAC instances, different transceiver components, and/orindependent combinations thereof) and that the reconfigurations are notconflicting with each other. The WTRU may perform the RRC procedures inparallel based on determining that both procedures are independent innature (e.g. a measurement configuration and a reconfiguration ofdedicated resources). For example, the WTRU may determine that theprocessing requirement (e.g., in terms of maximum delay) to complete theprocedure(s) are the same as for the case where each procedure wouldhave been performed separately. Otherwise, the WTRU may be configured toperform synchronization with the network (e.g., by performing a RACHprocedure). For example, if timing uncertainty is introduced for boththe MeNB and SCeNB for an RRC procedure due to the configuration of dualconnectivity, the WTRU may be configured to perform a RACH procedure forone or more RRC procedures that modify the corresponding physical layerparameters of the WTRU and/or for each of the reconfigured physicallayers.

In an example, the WTRU may be configured to process the second messageonce the ongoing procedure has completed, such that RRC procedures areperformed sequentially. For example, the WTRU may determine to performthe RRC procedures sequentially based on determining that both RRCprocedures are independent from each other. In an example, the WTRU maydetermine that the ongoing procedure should be suspended such that theother RRC PDU should be prioritized based on one or more of the identityof the eNB(s) associated with the RRC procedures, an identity of the SRBassociated with the RRC procedure, the type of RRC PDU that is received,the type of RRC procedure, and/or the like.

For example, the WTRU may determine which RRC procedure toprioritize/perform first as a function of the identity of eNB (and/orlayer/Uu interface) associated with the RRC procedure. For example, theWTRU may prioritize a procedure associated with a MeNB over that of anSCeNB. For example, the WTRU may suspend (or stop, or complete with afailure) the ongoing procedure in favor of initiating a new procedure ifthe new procedure is for the MeNB/primary layer and the ongoingprocedure is for the SCeNB/secondary layer.

For example, the WTRU may determine which RRC procedure toprioritize/perform first as a function of the identity of the SRBassociated with the procedure. The WTRU may determine that the SRB forwhich the RRC PDU is received is of higher priority that that associatedwith the RRC PDU that initiated the ongoing procedure. For example, theWTRU may prioritize the processing of a RRC PDU associated with SRB0,SRB1, or SRB2 over an RRC procedure initiated from a RRC PDU associatedwith SRB3.

The WTRU may determine which RRC procedure to prioritize/perform firstas a function of the type of procedure associated with the received RRCPDU(s) and the ongoing RRC procedure. For example, the WTRU mayprioritize an RRC PDU associated with a mobility event or to a securityevent over the completion of an ongoing procedure associated with areconfiguration of a secondary layer.

The WTRU may be configured to drop and/or initiate a failure procedurefor an ongoing RRC procedure that conflicts with a RRC PDU that receivedand determined to have a higher priority. The WTRU may be configured toignore an RRC PDU associated with a lower priority if a higher priorityRRC procedure is ongoing. For example, the WTRU may determine that asecond RRC PDU should be ignored and/or that the WTRU should proceed tofailure logic for an RRC procedure associated with the second RRC PDUbased on determining that another RRC procedure invalidates and/orconflicts with the RRC procedure associated with the second RRC PDU andthat the other RRC procedure has a higher priority than the RRCprocedure associated with the second RRC PDU. For example, the WTRU maydrop an RRC PDU or initiate failure logical for an RRC procedureassociated with the RRC PDU based on determining that the procedures aredependent on each other. For example, the WTRU may have an ongoingmobility procedure based on receiving an RRC reconfiguration messagewith the mobilityControlInfo IE (e.g., a handover command) thatinstructs the WTRU to remove the configuration associated with an SCeNBand to perform a handover to another cell for the RRC Connection. Insuch a case, the WTRU may process and perform the mobility procedure(e.g., associated with the handover command) and determine that thereconfiguration procedure for the SCeNB is invalid. In an example, theWTRU may transmit a message indicating the failure to perform the secondprocedure, and the message may include an indication of the cause of thefailure (e.g., “override by MeNB”).

In an example, the WTRU may suspend an ongoing RRC procedure if theongoing procedure conflicts with an RRC PDU received for another layerand completion of the ongoing RRC procedure would result in asynchronization event with the concerned eNB (e.g., completion of theRRC procedure would result in a RACH procedure).

The WTRU may be configured to perform one or more actions uponreconfiguration failure for a secondary layer and/or upon determining toinitiate a reconfiguration failure procedure (e.g., due to conflictsbetween multiple RRC procedures). The WTRU may determine that areconfiguration of a given layer has failed based on one or more offailure to interpret and/or decode a reconfiguration message, failure tosuccessfully apply a configuration provided during a reconfigurationprocedure, failure to successfully perform random access using newconfiguration, determining a received configuration exceeds thecapabilities of the WTRU (e.g., a received configuration cannot beapplied based on WTRU capabilities), detection of conflicting controlplane signaling, detecting RLF, and/or the like. If the WTRU determinesthat it was unsuccessful in configuring one or more (or all) servingcell(s) for a secondary layer and/or MAC instance, the WTRU may performvarious actions. For example, if the WTRU determines that an RRCconnection reconfiguration procedure has failed, the WTRU may revert toa previous configuration for the secondary layer (e.g., if the case thereconfiguration had failed for the secondary layer and/or a singlelayer). In an example, the WTRU may return to the primary layer and stoputilizing configurations for secondary layers (e.g., in the case ofmobility failure for all secondary layers). The WTRU may initiate a RRCConnection Re-establishment procedure in the primary layer, for exampleto re-establish radio bearers (e.g., DRBs, perhaps DRBs and not SRBs)associated with the secondary layer for which the reconfiguration hadfailed. For example, the WTRU may perform a re-establishment procedurefor all DRBs associated with a secondary layer for which areconfiguration failure occurred and/or for the specific DRBs of thesecondary layer that were the subject of the failed reconfigurationprocedure. As an example, the WTRU may send an indication of why thereconfiguration failure occurred to the network. For example, if thereconfiguration failure occurred because it conflicted with another RRCprocedure being implemented by the WTRU (e.g., for another layer), theWTRU may indicate that a conflict has occurred, for example byindicating the cause as “WTRU capabilities exceeded” or somesimilar/other cause. The WTRU may initiate the transmission of ameasurement report to the macro layer upon determining a reconfigurationprocedure for a secondary layer has failed. For example, the report mayinclude one or more measurement results for the layer that failedreconfiguration. As an example, the WTRU may determine that the WTRUfailed to configure a secondary layer if the WTRU fails to successfullyapply a configuration for the PCell of the secondary layer. For example,the WTRU may determine that it has failed to successfully synchronizewith the PCell and/or if it has failed to successfully perform randomaccess on the PCell. Such failures may cause the WTRU to consider thereconfiguration to be a failure.

The WTRU may be configured to perform an RRC connection re-establishmentprocedure, for example based on the failure to successfully reconfigureone or more layers. The following examples may be used for an RRCConnection (or secondary layer) Re-establishment Procedure. For example,the WTRU may determine that some or all serving cells of a secondarylayer (e.g., the PCell of a secondary layer) are experiencing radio linkproblems. The WTRU may detect a failure conditions that may indicatethat transmissions for the DRBs of a secondary layer will beunsuccessful or no longer possible. For example, if DRBs are exclusivelyassociated with a secondary layer, and one or more cells of thesecondary layer are experiencing radio link problems (e.g., RLF has beendeclared), the WTRU may determine that is will be unable to communicateusing the bearers. As an example, a re-establishment procedure may beperformed for DRBs for which the QoS may no longer be met, but not forDRBs for which the QoS can still be met. RRC re-establishment may beperformed for SRBs (e.g., SRB3). For example, a re-establishmentprocedure may be performed for an SRB associated with a secondary layerif the re-establishment procedure indicates that a secondary layer isstill used for the concerned RBs after the completion of the procedure.The re-establishment procedure may be when a primary layer (e.g., thePCell of a primary layer) is experiencing radio link failure and/or whena secondary layer (e.g., the PCell of a secondary layer) is experiencingradio link failure.

For example, the WTRU may determine that a re-establishment procedureshould be performed for a given layer based on detecting one or morefailure conditions. Examples of failure conditions may include one ormore of DL RLF, UL RLF, handover failure for a secondary layer, securityfailure (e.g., integrity verification failure), an indication from lowerlayer (e.g., MAC) that a configuration and/or reconfiguration procedurehas failed, a reconfiguration failure that associated with areconfiguration of a secondary layer, and/or other failure situations.In case of failure conditions being detected for a given layer, the WTRUmay attempt to initiate a re-establishment request in a cell of a layerthat is not in a failure condition. For example, the re-establishmentmay be to a cell of a layer has been configured for use by the WTRU, butthat may be in a deactivated/idle state. In an example, the WTRU mayattempt to perform re-establishment in a configured and active layerthat is different than the layer in which the failure was detected. Forexample, if the cell used for the re-establishment procedure waspreviously inactive, the WTRU may first resume normal operation and/oractivate the concerned cell. For example, the inactive layer may be acell (e.g., the PCell) of the primary layer. In an example, are-establishment request may be initiated to a secondary layer cell.

For example, upon detecting a failure in a cell of a given layer (e.g.,a secondary layer), the WTRU may initiate a re-establishment procedure,for example in a cell of the primary layer and/or the cell of adifferent secondary layer. The WTRU may suspend one or more DRBsassociated with the layer for which the re-establishment is beingperformed (e.g., DRBs associated with a failed secondary layer). In anexample, the WTRU may release all cells of the layer for which there-establishment is being performed. The WTRU may reset (e.g., and/ortear down) the MAC instance that corresponds to the layer for which there-establishment is being performed. For example, the WTRU may initiatethe transmission of an RRC message (e.g., an RRC connectionre-establishment (or similar) message that indicates a “layer failure”),which may include the identity of the layer for which there-establishment is being performed (e.g., in reestablishmentCause). Ifthe re-establishment procedure was triggered based on an eventconfiguration, the WTRU may include a measID and/or an indication of“decreasing quality” and/or “insufficient quality.” If the WTRU performsthe re-establishment via a layer that is in a deactivated/idle state,the WTRU may include an identity, for example such as a WTRU identityand/or a context identity. For example, the identity may be a valueassigned to the WTRU in the configuration of the layer for which there-establishment is being performed and/or the layer over which there-establishment procedure is being performed. As an example, theidentity may be a C-RNTI assigned to the WTRU in the configuration ofthe layer for which the re-establishment is being performed and/or thelayer over which the re-establishment procedure is being performed.

The WTRU may receive an RRC Connection Reconfiguration message. Thereconfiguration messages may re-associate one or more DRBs to a layerwhere a failure condition was not detected (e.g., to the primary layer).The WTRU may tear down and/or remove the configuration for a MACinstance that corresponds to the layer that failed. In an example, thereconfiguration message may re-associate the DRBs of the failed layer(e.g., and/or SRBs) to a new secondary layer and/or to the primarylayer. The WTRU may reuse the MAC instance that corresponds to the layerthat failed for a new secondary layer and/or may instantiate a new MACinstance for the newly configured secondary layer. Whether a primarylayer or a secondary layer is to be used for the re-association of theRBs may be indicated using a layer identity that is included in thereconfiguration message.

If the WTRU is configured to perform a reconfiguration (e.g., based onperforming layer reestablishment, based on occurrence of a mobilityevent, based on activation/deactivation of a layer, etc.), the WTRU mayre-establish PDCP for the DRBs associated with the layer beingreconfigured (and/or for the SRBs of the layer being reconfigured). Forexample, if the PDCP instance is WTRU-specific (e.g., such as in anarchitecture in which the receiving/transmitting PDCP entities arechanged upon mobility event in the primary layer, but not upon mobilityevent associated with the secondary layer(s)), the WTRU may re-establishPDCP by performing a subset of the PDCP re-establishment procedure thatwould be performed if the primary layer was to be re-established. Forexample, the WTRU may skip PDCP re-establishment, meaning that the WTRUmay continue the header compression protocol without resetting it, maymaintain the security context and/or may continue the sequencinginformation unaffected. In an example, the WTRU may transmit a PDCPstatus report in the uplink, if configured. The WTRU may re-establishRLC for the concerned DRBs (and/or SRBs, if applicable).

Upon successful completion of a reconfiguration procedure based on thefailure of a secondary layer, the WTRU may determine that there-establishment of the DRBs for the layer that failed was successful.The WTRU may resume using any suspended RBs for the layer that failed,for example on a different layer as set by the reconfigurationprocedure. The WTRU may include a status report indicating user planedata that has yet to be successfully transmitted/received once itresumes the DRBs that were reconfigured. The WTRU may perform are-establishment request for DRBs of a secondary layer if it determinesuplink radio link failure. In an example, re-establishment for DRBs of asecondary layer may be performed for the PCell of a secondary layer, butnot for SCells of a secondary layer.

As the different serving sites are able to provide access and servicesto a WTRU relatively independently of each other, WTRU behavior withinsuch an architecture may be different that WTRU behavior in a singledata path architecture. For example, a WTRU may be connect to a first,primary serving site (MeNB). The WTRU may establish an RRC connectionwith the primary serving site in a manner similar to Release 11. Duringthe connection process, the WTRU may send an indication to the networkthat indicates that the WTRU supports multi-serving site connectivity.Based on receiving the indication, the network may preconfigure the WTRUto access one or more secondary serving sites. For example, the primaryserving site may send an RRC Connection Reconfiguration message to theWTRU. The RRC Connection Reconfiguration message may include anindication that the reconfiguration is to add additional MAC instancesand/or to add additional transmission layers.

The WTRU may store the configuration information for one or more layers.However, although the received configuration(s) may be valid, the actualconnections between the WTRU and the preconfigured serving sites may bedeactivated. The configuration information stored by the WTRU may bestored and/or remain valid until the WTRU receives a message thatremoves, changes, and/or releases the configuration. In an example,stored configuration information may be valid for a set period of time,and an indication of the period of time may be part of theconfiguration. The WTRU may be considered valid until a specified eventoccurs (e.g., until cell re-selection occurs in a primary layer). Forexample, the stored configuration information may be considered validuntil a mobility event occurs (e.g., the WTRU moves to a different PLMN,a different tracking area, etc.).

The configuration of a primary layer may be valid for different periodsof time than a configuration of a secondary layer. For example, an eventmay trigger the WTRU to disregard the configuration of the secondarylayer, but not the primary layer (or vice versa). A network may“pre-configured” or “prepare” a WTRU with configuration information forone or more layers (e.g., a primary layer, a secondary layer, etc.)without activating the one or more layers. The network may then sendsignaling to the WTRU to indicate that the WTRU should activate one ormore preconfigured layers. The WTRU may prioritize a configuration of afirst layer over a configuration of a second layer. For example, theWTRU may prioritize the configuration of the primary layer (e.g., whichmay correspond to a macro layer and/or be served by a MeNB) forfunctions such as connection re-establishment and/or mobility if anotherlayer fails (e.g., a secondary layer).

The configuration information for multiple layers may configure the WTRUto utilize a plurality of MAC instances. Depending on the circumstancesunder which the WTRU is attempting to access the different servingsites, the WTRU may be configured to maintain a different number ofactivate serving sites at any given instance in time. For example, theWTRU may have a single MAC instance (or layer) active at any given time.A configuration where a single MAC instance (or layer) is active at anygiven time may be referred to as single MAC connectivity. The WTRU maymaintain a single active layer, for example which ever layer providesthe best connectivity at a given time instance. For example, small celllayers may be used to achieve throughput gains and/or may be used tooffload traffic from a macro layer. If the small cell layers are beingused for macro layer offload, then the WTRU may deactivate the primarylayer after activating and accessing a secondary layer.

For example, as noted above the WTRU may first connect the macro layer.After receiving preconfiguration information for one or more potentialsecondary layers, the WTRU may activate a secondary layer and beginaccessing the secondary serving site. The WTRU may then deactivate theconnection to the primary serving site while maintaining the connectionto the secondary serving site. In this manner, the WTRU may effectivelybe offloaded from the macro layer while maintaining continuous servicein the small cell layer.

In an example, if the primary layer is inactive and/or is not used fortransmission and/or reception of data, the configuration/context for theprimary layer may be stored in the WTRU, but the WTRU may refrain fromutilizing the configuration/context for the primary layer fortransmissions. The primary layer configuration and/or configurationsassociated with serving cells for the primary layer may be considered asidle or as deactivated but may be kept in memory for subsequentreactivation and use. The WTRU may receive control signaling thatdeactivates one or more layers and/or activates one or more layers. Inan example, the deactivation of a certain layer may trigger the WTRU toactivate a different layer.

During the period when the macro layer is deactivated, the WTRU maycontinue to monitor the macro layer serving site. For example, mobilityrelated procedures and/or the WTRU RRC connection may be associated withthe WTRU connection to the primary serving site. Offloaded data transfermay be performed via the one or more active secondary serving sites. Toensure the WTRU is still able to access the macro serving site in casethe macro layer is reactivated (e.g., to perform a mobility or othercontrol procedure, to send and/or receive data, etc.), the WTRU maycontinue to measure the macro serving site (e.g., MeNB). The WTRU mayperform the monitoring based on one or more triggers. For example, thedetermination to perform measurements on the macro serving site (e.g.,and/or on one or more other deactivated layers) may be based on one ormore triggers. The triggers for performing such measurements aredescribed in more detail below. Similarly, the trigger(s) to send ameasurement report including information related to the qualitymeasurements performed on the WTRU may be defined. The trigger(s) forsending a measurement report may be the same or different than thetrigger(s) for performing the measurements. For purposes of explanationand conciseness, the examples of trigger(s) for performing measurementsand the trigger(s) for sending measurement report may be describedtogether herein. However, it is contemplated that various combinationsof triggers may be used to trigger measurement performance andmeasurement reporting. For example, a first trigger such as the qualityof the serving cell of an active layer falling below a threshold maytrigger the WTRU to perform measurements on a deactivated serving cellof another layer. A second trigger such as the quality of the servingcell of the another layer being above a threshold and/or better than thecurrent serving cell of the active layer by a predetermined thresholdmay cause the WTRU to report the measurements of the serving site of thedeactivated layer to the network (e.g., the active serving site). Theactive serving site may use the measurement information to instruct theWTRU to activate one or more deactivated layers. For example, theprimary serving site may send MAC signaling (e.g., a MAC CE) to WTRUthat indicates a preconfigured, deactivated secondary layer is to beactivated. The MAC signaling may indicate that one or more layers (e.g.the currently activated primary layer) should be deactivated uponactivation of the other layer and/or the WTRU may implicitly determineto deactivate an active layer based on activating the other layer.

Further, rather than or in addition to activation and deactivation oflayers being triggered by explicit signaling from the network, one ormore preconfigured layers may be autonomously activated and/ordeactivated by the WTRU. For example, rather than or in addition tosending measurement reports of deactivated serving sites to the network,the WTRU may locally evaluate the measurements to determine whether adeactivated layer should be activated and/or a activated layer should bedeactivated. Since the WTRU may be use similar criteria as the networkfor evaluating whether a layer should be activated or deactivated, thetriggers for WTRU autonomous activation and/or deactivation may besimilar to the triggers that are described for causing the WTRU toperform measurements or a deactivated layer and/or send measurementreports to the network (e.g., an active serving site). Therefore, forpurposes of explanation and conciseness the triggers for causing theWTRU to autonomously activate and/or deactivate a layer may be describedin combination with the triggers for the WTRU to perform measurementsand/or send measurement reports. However, as may be appreciated, variouscombinations of such triggers may be implemented such that a first setof triggers may cause the WTRU to perform measurements, a second set oftriggers may cause the WTRU to report the measurements, and a third setof triggers may cause the WTRU to autonomously activate and/ordeactivate a layer. The first, second, and/or third sets of triggers mayeach be different, may be partially overlapping, and/or may becompletely overlapping (e.g., the triggers to perform measurements maybe the same as the trigger to report measurements). Various combinationsof the triggers—although described together herein—are within thecontemplated scope of this disclosure.

In an example, the WTRU may be configured to activate or use more thanone MAC instance (or layer) at a given time. For example, a first MACinstance may be active and configured for transmission/reception over aprimary layer and a second MAC instance may be active and configured fortransmission/reception over a secondary layer. The different MACinstances may be active simultaneously at some points in time, while asingle MAC instance may be active at other points in time.

The WTRU may perform layer deactivation. For example, the WTRU mayreceive control signaling that deactivates a given cell of a given layer(e.g., a Primary Cell (PCell) in the layer, a secondary cell (SCell) inthe layer, etc.) multiple cells of a given layer, and/or all cells of agiven layer. The WTRU may be configured to perform carrier aggregationin the different layers, for example such that the WTRU may transmitand/or receive data from multiple cells associated with a layer.However, unlike layered transmission using multiple data paths, carrieraggregation may be characterized in that each of the transmissions sentfrom a cell/carrier being aggregated by be scheduled by the same entityor may be scheduled by independent entities in a coordinated fashion(e.g., there may be a low latency communication interface between thescheduling entities). For transmission over different layers or datapaths, the independent scheduling entities lack tight coordinationand/or may communicate via a communication link whose latency makes itdifficult and/or impractical to coordinate the scheduling of the WTRUacross the layers. A PCell may refer to a primary cell of a layer, whichmay be the cell through which carrier aggregation for the layer isconfigured or established. Each layer may additionally utilize one ormore SCells, which may be carrier aggregation cells/carriers associatedwith the layer. The PCell may be used to schedule transmissions on theSCell and/or the transmissions may be scheduled directly via the Scell.The WTRU may be configured to deactivate PCells and/or SCellsautonomously, for example, upon expiration of a timer after a period ofscheduling inactivity for the concerned cell.

Forming an RRC connection may establish one or more signaling radiobearers (SRBs) between the WTRU and the network, for example such thateach of the established SRBs may be assigned to one or more of the firstradio interface or the second radio interface. The control data receivedby the WTRU over the may be include in one or more RRC protocol dataunits (PDUs). An RRC PDU may be associated with one of the one or moreSRBs. In an example, the RRC PDU may be received over either the firstradio interface or the second radio interface irrespective of itsassociated SRB. In another example, the RRC PDU may be received over theassigned radio interface associated with the corresponding SRB. The RRCconnection may be controlled by the network. The network may comprise aRadio Cloud Network Controller (RCNC) that controls the RRC connection.The WTRU may transmit an indication to the network indicating that theWTRU supports multi-scheduling operation.

In an example, a WTRU may be configured to operate using one or moreSRBs associated a MeNB or cells served by the MeNB (e.g., may bereferred to a macro(SRB)), one or more SRBs associated a SCeNB or cellsserved by the SCeNB (e.g., may be referred to a sc(SRB)), one or moredata radio bearers (DRBs) associated a MeNB or cells served by the MeNB(e.g., may be referred to a macro(DRB)), and or one or more DRBsassociated a SCeNB or cells served by the SCeNB (e.g., may be referredto a sc(DRB)). In an example, the WTRU may establish a macro(SRB) with aMeNB and establish a sc(SRB) and a sc(DRB) with a SCeNB.

For example, a MAC instance at the WTRU may be configured and active forthe secondary layer, and may be used for both user plane (e.g., sc(DRB))and control plane (e.g., sc(SRB)) data. In some scenarios, transmissionand/or reception may be more frequently performed using the SCeNB, sothe secondary layer may be considered the main layer to perform data andcontrol plane data transmission/reception and/or physical layerprocedures. Even when the majority of data transmissions are sent viathe SCeNB, the WTRU may still have configured a MAC instance for theprimary layer, for example that may be used for control plane data(e.g., for traffic that may be sent via either layer, for traffic thatmay be sent through the primary layer only, etc.). In some scenarios,the primary layer MAC instance may be active at the same time as thesecondary layer MAC instance, which may be referred to as dual MACconnectivity. The macro(SRB) may be utilized for transmission ofrelatively high importance control information, so in some examples theWTRU may be configured to refrain from deactivating the PCell of theprimary layer (and/or the entire primary layer) in order to ensure thatmacro(SRB) data is timely delivered. However, in other examples, suchcontrol information may be deliverable via a secondary layer, so duringperiods of inactivity the primary layer may be deactivated and/or mayoperate according to IDLE mode principles in order conserve power andnetwork resources. In, the WTRU may be configured to periodically orintermittently monitor a control channel (e.g., PDCCH for Random AccessChannel (RACH) orders, a paging channel, etc.) even if a secondary layeris active and/or if the primary layer has been deactivated.

In an example, the WTRU may be configured to exchange control plane datausing the primary layer (e.g., via a macro(SRB)) and user plane data viaa secondary layer (e.g., via a sc(DRB)). Such a scenario may be the casewhen, for example, a WTRU was offloaded from a MeNB to a SCeNB for datatransfer. The MAC instance that is configured and active for the primarylayer may be used remain active and be used for transmission of controlinformation. A MAC instance may be configured and active for a secondarylayer and may be used to transfer user plane data. The macro(SRB) may beutilized for transmission of relatively high importance controlinformation, so in some examples the WTRU may be configured to refrainfrom deactivating the PCell of the primary layer (and/or the entireprimary layer) in order to ensure that macro(SRB) data is timelydelivered. However, in other examples, such control information may bedeliverable via a secondary layer, so during periods of inactivity theprimary layer may be deactivated and/or may operate according to IDLEmode principles in order conserve power and network resources. In, theWTRU may be configured to periodically or intermittently monitor acontrol channel (e.g., PDCCH for Random Access Channel (RACH) orders, apaging channel, etc.) even if a secondary layer is active and/or if theprimary layer has been deactivated.

Regardless of how the data and control information is transferred to theWTRU (e.g., via one or more of the primary and/or secondary layers), theWTRU may be configured to maintain or store configuration informationfor each of the layers/MAC instances even after deactivating a MACinstance. For example, the WTRU may be configured to store configurationfor the primary layer even after deactivation of the primary layer. Inthis manner, the WTRU may be able to quickly return to the macro layereven if it has been deactivated. Quickly returning to the macro layermay allow for fast recovery from radio link failure (RLF) at thesecondary layer and may facilitate the avoidance of radio link failuresin handover scenarios between small cells.

RRC signaling may be utilized to configure primary layer and/orsecondary layer operation. The layer configuration may include one ormore of PHY configuration information, MAC configuration information,RLC configuration information, PDCP configuration information, radiobearer (RB) configuration information, Cell Radio Network TemporaryIdentifier (C-RNTI) information, etc. The configuration informationprovided for the primary layer may include of full set of configurationinformation (e.g., PHY configuration information, MAC configurationinformation, RLC configuration information, PDCP configurationinformation, RB configuration information, C-RNTI information, etc.)that allows the WTRU to perform transmission and reception procedures inthe primary layer. In an example, the WTRU may also be configured with asubset of configuration information for transmitting and reception inthe secondary layer. For example, the WTRU may be configured with MACconfiguration information, RLC configuration information, PDCPconfiguration information, and a subset of PHY layerresources/configuration information to be used in the secondary layer.Other configuration information such as the remaining PHY layerresources/configuration information (e.g., such as PUCCH configurationinformation, etc.) may be included in a reconfiguration message that issent in order to activate the secondary layer. In this manner the WTRUmay be preconfigured with the majority of the configuration informationfor using the secondary layer and certain configuration information maybe provided upon activation (e.g., to ensure the configuration does notconflict with the current configuration being utilized at the primarylayer).

The primary layer configuration may include full configurationinformation associated with the operation of both SRBs and DRBs on thatlayer or may include a subset of the configuration (e.g., only theSRBs). The subset of the configuration may allow the WTRU to perform oneor more of receiving data associated with an SRB, receiving an RRCreconfiguration message, perform a handover, and/or perform areconfiguration procedure.

The WTRU may be configured to, upon receiving a configuration for asecond layer (and/or the remaining configuration information such as PHYinformation that was not provided as part of an initialpre-configuration), implicitly determine to activate the second layerand may begin using the secondary layer as the active layer. The WTRUmay store the configuration for the primary layer upon activation of thesecondary layer so that the primary layer can be reactivated at a latertime. In another example, the WTRU may implicitly assume that theprimary layer is the active layer (and store the context of the inactivelayers in memory for later use) until the network explicitly indicatesthat another layer is the active layer. The context stored in the WTRUfor the inactive layer may be considered valid until explicitly deletedby the network. The configuration information may be considered validfor a defined period of time. The configuration information for asecondary layer may be deleted upon a change to a different secondarylayer and/or upon a change to a primary layer.

When operating using a secondary layer, the WTRU may store thecontext/configuration information of the primary layer and consider theprimary layer to be deactivated and/or in idle mode. In an example,rather than completely deactivating the primary layer, the WTRU may havean independent discontinuous reception (DRX) configuration to keep thecontext of the primary layer alive. During the DRX period, the WTRU mayperiodically check cells associated with the primary layer fortransmissions (e.g., read the PDCCH). The WTRU may monitor a deactivatedlayer during the active periods of the DRX cycle even if it is activelymonitoring/utilizing a different layer. The WTRU may also be providedwith an explicit indication as to which layer is initially active at thetime of the receiving the RRC configuration information. Thus, the RRCconnection reconfiguration information may include configurationinformation for a plurality of layers, and may further indicate which ofthe layers is initially active. The WTRU may then store configurationinformation for the inactive layers for later use while using theconfiguration of the active layer to perform reception and transmissionprocedures.

One or more triggers may cause the WTRU to activate the primary layer,activate an inactive layer, and/or report quality information for one ormore layers. For example, while the WTRU is operating with a secondarylayer as an active layer, the WTRU may be triggered to use (or returnto) the primary layer (e.g., for user plane and/or control planetransmission and/or reception) in order to receive an RRCreconfiguration message. For example, the RRC reconfiguration messagemay indicate that the WTRU is to perform a handover, may be designed tohelp the WTRU avoid radio link failure, may facilitate the performanceof a fast re-establishment to the primary layer, and/or the like. Theswitch to the primary layer may be temporary (e.g., the WTRU may switchback after receiving the control plane data), and the WTRU may beconfigured to utilize a Pcell of the primary layer in order to receivethe control plane data.

In an example, the WTRU may receive explicit, dynamic signaling from thenetwork that triggers the WTRU to switch layers, activate a given layer,and/or deactivate a given layer. For example, a PDCCH order and/or MACcontrol PDUs (e.g., MAC control elements (CEs)) may be used to indicateto the WTRU to switch layers, activate a layer, and/or deactivate alayer. As an example, the WTRU may receive a PDCCH order or a MACcontrol PDU that indicates that the WTRU should deactivate a currentlyactive MAC instance (e.g., layer) and/or activate a different MACinstance/layer. The explicit activation indication may explicitlyindicate which layer should be activated or the WTRU may implicitlydetermine which layer is to be activated.

Various implicit criteria may be used by the WTRU to determine toactivate an inactive/idle layer (e.g., the primary layer), switch to aninactive/idle layer (e.g., the primary layer), and/or to deactivate agiven layer. For example, the WTRU may begin monitoring a previouslyinactive (e.g., begin reading or monitoring the inactive layer PDCCHusing a stored C-RNTI for the inactive layer) based on detecting variouscriteria. In an example, although the WTRU may begin someprocessing/monitoring of an inactive layer based on detecting implicittriggers, the WTRU may be configured to refrain from switching to thelayer or fully activating the layer until an explicit indication to doso is received from the network (e.g., via a PDCCH order or MAC ControlPDU).

For example, the downlink quality as observed by the WTRU may be used asan implicit criteria to determine to begin monitoring (e.g., partiallymonitoring) an inactive layer and/or to report an indication of thedownlink quality of an inactive layer to the network. The followingcriteria may be described for triggering the WTRU to send a measurementreport for an inactive layer; however, such triggers may also be used totrigger the WTRU to begin monitoring an inactive layer (e.g., monitoringa PDCCH of cell in the inactive layer). Additionally, such criteria mayalso be applicable to trigger the WTRU to activate and/or deactivate alayer.

For example, the WTRU may monitor the downlink quality of one or morelayers for which it has received configuration information but that arecurrently not active. There may be one or more triggers that cause theWTRU to perform measurements on a cell associated with the inactivelayer (e.g., such triggers may also cause the WTRU to begin monitoringthe cell for transmissions, activate and/or deactivate various cells,and/or the like). For example, the WTRU may be configured to performmeasurements on a cell associated with the inactive layer any time ameasurement report is triggered (e.g., for another layer/cell or for theinactive layer/cell). In an example, the WTRU may be configured toperform measurements on a cell associated with the inactive layer basedon a specified event occurring (e.g., a handover, an event indicated inthe configuration, etc.).

The WTRU may be configured to perform measurements on a cell associatedwith the inactive layer (e.g., primary layer) when a measurement reportis triggered in the active layer (e.g., secondary layer) and the qualityof the active layer is below a predetermined threshold (e.g., indicatingthat the WTRU is losing coverage in the active layer). For example, theWTRU may determine that the quality of the active layer is deterioratingand/or that measurements should be performed on the inactive layer basedon one or more of Reference Signal Receive Power (RSRP) measurements forthe active layer falling below a threshold, the Reference SignalReceived Quality (RSRQ) measurements for the active layer falling belowa threshold, the determined channel quality indicator (CQI) for a cellassociated with the active layer being below a threshold, the determinedCQI for a serving cell of the active layer (e.g., of the serving cellfor the SCeNB) being below a threshold and the determined CQI for anon-serving cell of the active layer (e.g., some other cell associatedwith the SCeNB) being above a threshold, and/or the WTRU starting theT301 timer (e.g., upon detecting the deteriorations of radio linkconditions).

In an example, the WTRU may be configured to perform measurements on acell associated with the inactive layer (e.g., primary layer) based on ameasurement report indicating that the best cell (e.g., highest qualitycell) in the currently active layer (e.g., the secondary layer) haschanged. The WTRU may be configured to perform measurements on a cellassociated with the inactive layer based on a measurement reportindicating that the best cell (e.g., highest quality cell) in theprimary layer has changed. In an example, the WTRU may be configured toperform measurements on a cell associated with the inactive layer (e.g.,primary layer) based on a measurement report being triggered or sent andthe active MAC instance being out-of-synch (e.g., upon start of T310and/or upon start of T311, etc.). The WTRU may be configured to performmeasurements on a cell associated with the inactive layer (e.g., primarylayer) based on failing to receive a handover command withinpredetermined period of time while the quality of active layer is belowa threshold.

In an example, the WTRU may be configured to perform measurements on acell associated with the inactive layer (e.g., primary layer) based ondetecting an out-of-synch condition in the active layer and/or based ondetecting a predetermined number of out-of-synch conditions in theactive layer. The WTRU may be configured to perform measurements on acell associated with the inactive layer (e.g., primary layer) based onan out-of-synch condition being detected in the active layer for anetwork configured period of time and/or based on an out-of-synchcondition being detected a given number of timers within a predeterminedwindow. In an example, the WTRU may be configured to performmeasurements on a cell associated with the inactive layer (e.g., primarylayer) based on detecting one or more of DL RLF and/or an UL RLF in theactive layer. In an example, the WTRU may be configured to performmeasurements on a cell associated with the inactive layer (e.g., primarylayer) based on the WTRU losing timing alignment with currently activelayer (e.g., timing alignment timer (TAT) expiry, for example whereinthe TAT of the PCell of the active layer expires if multiple TimingAdvance Group are configured for the concerned layer). In an example,the WTRU may be configured to perform measurements on a cell associatedwith the inactive layer (e.g., primary layer) based on detecting ascheduling request (SR) failure. For example, the WTRU may attempt tore-establish connectivity on an inactive layer (e.g., the primary layer)before attempting to perform an RRC connection re-establishmentprocedure on the currently active layer. In an example, the WTRU may beconfigured to perform measurements on a cell associated with theinactive layer (e.g., primary layer) based on the quality of an inactivelayer being above a threshold for a configured period of time. In anexample, the WTRU may be configured to perform measurements on a cellassociated with the inactive layer based on the quality of the servingcell of primary layer or the quality of the serving cell of an activelayer being below a threshold and no other cells the layer being above athreshold (e.g., active layer is losing coverage).

In an example, the WTRU may be configured to perform measurements on acell associated with the inactive layer (e.g., primary layer) based onreceiving a deactivation command for the active layer (e.g., which maybe an implicit activation of the primary layer). In an example, the WTRUmay be configured to perform measurements on a cell associated with theinactive layer (e.g., primary layer) based on the WTRU receiving an RRCreconfiguration message (e.g., the message may de-configure ordeactivate the active layer. In an example, the WTRU may be configuredto perform measurements on a cell associated with the inactive layer(e.g., primary layer) based on the estimated rate of change in qualityof the channel on the active (e.g., secondary layer) being (and/orbecoming) higher than a threshold for a configured period of time. Forexample, the rate of change of the channel may be estimated by measuringa reference signal transmitted from the active (e.g., secondary) layer.Other measure of the rate of change of the channel may be based on aDoppler spread of the channel and/or an absolute value of the Dopplershift of the channel. An estimated rate of change of the channel may beproportional to (and based on) the multiplicative inverse of thecoherence time of the channel. In an example, the WTRU may be configuredto perform measurements on a cell associated with the inactive layer(e.g., primary layer) based on the estimated rate of change of thefading-averaged path loss on the currently active (e.g., secondary)layer being (or becoming) higher than a threshold for a configuredperiod of time. For example, the rate of change of the fading-averagedpath loss may be estimated by subtracting the time-averaged receivedpower level of a reference signal of a first time window from that of aprevious time window. In an example, the WTRU may be configured toperform measurements on a cell associated with the inactive layer (e.g.,primary layer) based on receiving an indication from RLC that a maximumnumber of retransmissions has been reached. In an example, the WTRU maybe configured to perform measurements on a cell associated with theinactive layer (e.g., primary layer) based on receiving a random accessproblem indication from the MAC.

The WTRU may start monitoring a PDCCH associated with the primary layeror an inactive layer using a stored C-RNTI based on detecting one ormore of the conditions used to trigger measurements of the inactivelayer. However, in an example the WTRU may refrain from switching to theinactive layer and/or from performing full activation of the inactivelayer unless an explicit indication is received (e.g., via a PDCCH orderand/or MAC Control PDU) indicating that a switch or activation should beperformed.

The WTRU may be configured with a measurement configuration that is usedto determine parameters to use when performing measurements. Forexample, a measurement configuration may be common for all cells in alayer, common for all cells in a cluster (e.g., if clusters areutilized), configured separately for serving and non-serving cells perlayer, and/or configured separately for each cell in a given layer. Forexample, the WTRU may be configured with corresponding zero powerchannel state information reference signals (CSI-RSs) for differentcells/layers for CQI measurements. The WTRU may be configured with anaveraging time period, such that the measurements are performed andfiltered over the averaging period. The WTRU may be configured with theidentity of the node to which the report should be sent (e.g., MeNB,SCeNB, etc.). The WTRU may be configured with a periodicity to use forreporting measurement and/or may be configured with one or more triggersfor sending aperiodic reports (e.g., threshold values of channel qualityto trigger a report).

Layer-specific measurement configurations may be provided to the WTRU bythe network. For example, a received configuration or configurationparameter may explicitly indicate which layer the configuration isapplicable to. In an example, the measurement configuration may indicatea cluster ID that the measurement configuration is applicable to. Themeasurement configuration may include a list of cells that the WTRU mayperform measurement reporting for on a given layer and/or that the WTRUmay monitor. The measurement configuration may indicate a measurementcycle to be used for measuring cells within a layer based on theactivation and/or deactivation of another layer. For example, activationof a cell in a first layer may trigger more frequent measurements (e.g.,a fast measurement cycle) for neighboring cells. The measurementconfiguration may include a list of white listed cells that are neighborcells for a configured small-cell. In an example, if the small-cell isactivated (e.g., small cell layer is activated), WTRU may stop using themeasurement cycle measCycleSCell (e.g., the measurement cycle typicallyused for Scells in a deactivated stated), and may use a different (e.g.,a faster) measurement cycle. In an example, the activation of a firstcell may trigger a scaling down of the measCycleSCell to a smallervalue.

The WTRU may be configured to report the measurement information foreach cell it is currently monitoring, for a subset of cells, and/or forone or more clusters of cells. For example, which cells to measure maybe determine based on the cluster identity of the cell that triggeredthe report and/or the cell for which the measurement is being report.For example, the WTRU may be configured with a blacklist/whitelist inorder to determine which events trigger measurement reporting for cellsin a given cluster. For example, a measurement report may be triggeredfor a cell in a first cluster if the triggering is based on criteriaassociated with a cell of a different cluster (e.g., when measuring forinter-cluster mobility). In an example, the WTRU may be configured witha cluster identity such that the WTRU measures each of the cells in thecluster if measurements are triggered for any cell in the cluster.

The WTRU may send a report of quality measurements based on detecting atrigger to measure an inactive cell, periodically, and/or aperiodically(e.g., at the request of the network). The report may be sent to thenetwork node in the primary and/or secondary layer. For example, if theWTRU detects a trigger that may be used to trigger measurement of aninactive layer/cell, the WTRU may send a measurement report to thenetwork, and the measurement report may indicate what triggered thereport. Measurement reports may be sent periodically by the WTRU, forexample by configuring and setting a timer to be used to trigger thetransmission of a periodic report. The network may send a request for ameasurement report. The aperiodic measurement request may be sent to theWTRU, for example using one or more of a PDCCH order, a MAC control PDU,and/or an RRC measurement request. Aperiodic requests may be receivedfrom a primary layer (e.g., associated with a MeNB) and/or a secondarylayer (e.g. associated with a SCeNB). For example, the MeNB may requesta measurement report for cells belonging to any layer (e.g., primarylayer and/or a secondary layer). As an example, the SCeNB may send ameasurement request that indicate s that the WTRU should send ameasurement report to the MeNB (e.g., via RRC). The SCeNB may send therequest based on detecting radio link quality degradation (e.g., basedon UL RL quality, CQI reports received for the secondary layer beingbelow a threshold, etc.). A request for a measurement report may be sentby using PHY, MAC and/or RRC signaling. In an example, the request maybe sent by the SCeNB, for example, by use of a MAC CE.

The WTRU may provide the measurements and/or an indication of thequality of a cell/layer using on or more of an RRC message, a MACcontrol message, and/or a Layer 1 (PHY) message. For example, selectedmeasurements may be sent over an RRC measurement report and/or as partof an RRC establishment/re-establishment request. A MAC control message(e.g., MAC control element) may be used to send measurements. Forexample, a MAC CE may be used to send measurement information for eachreported cell along with the cell ID associated with the measurement(e.g., the measurements may be associated with the cell using theSCellIndex). If Layer 1 (PHY) reporting is utilized the report may betransmitted via the PUCCH.

For each reported layer/cell, the WTRU may send one or more of the RSRPof all cells being reported, the RSRP of cells on a reporting whitelist,and/or the RSRP of cells within a specified cluster for which the reportis performed. In an example, for each reported layer/cell the WTRU maysend one or more of the RSRQ of all cells being reported, the RSRQ ofcells on a reporting whitelist, and/or the RSRQ of cells within aspecified cluster for which the report is performed. The report mayinclude one or more of a CQI value measured for the cell, an identity ofthe cell that triggered the report; a list of DRBs that are served bythe layer that is experiencing failure, and/or an in-synch/out-of-synchindication.

The WTRU may be configured to and/or be requested by the network to senda measurement report in a variety of manners. For example, if the WTRUis configured to send the report via the primary layer and there is afailure on the primary layer, the report may be sent on another activelayer. For example, the report may be sent to an active small cell, andthe small cell node may forward it to the MeNB using the backhaul link.In an example, the WTRU may be configured to report measurements to theprimary layer, which may be associated with the macro eNB. In anexample, the report may be sent to both a primary layer and an activesecondary layer and/or all active layers. In an example, the report maybe via an RRC message to the primary layer (e.g., the macro layer), andthe MeNB may forward the information to other layers that may make useof the report. A measurement report may be sent to the same node wherethe request was received from. The node to which a measurement reportshould be sent may be configured and/or indicated by the receivedmeasurement reporting configuration. If measurement reporting isperformed over RRC, then if a secondary RRC is utilized by the secondarylayer (e.g., connected via the SCeNB), an appropriate SRB may beselected for sending the measurement information.

In an example, if the WTRU detects that radio link conditions havefallen below a configured threshold in the small-cell layer, the WTRUmay send a measurement report to the MeNB on another layer. For example,if the CQI of the active small cell layer are less than configuredthreshold, the WTRU may be triggered to send an indication regarding theradio conditions to the network.

In another example, the trigger to send measurement information to aprimary layer may be receipt of explicit signaling sent by the smallcell eNB, for example, by use of a MAC CE. For example, if the SCeNBdetects the WTRU CQI measurement has fallen below a threshold, it maysend a trigger to the WTRU RRC to send an aperiodic RRC measurementreport to the MeNB on another layer (e.g., the Macro layer). In anexample, the SCeNB may directly send an indication over the backhaul tothe MeNB or forward the measurement report from the WTRU to the Macro.

In an example, the measurement configuration may include a list ofwhite-listed cells. For example, the white-listed cells may be a list ofcells that are neighbor cells for the configured small-cell. If thesmall-cell/the small-cell layer is activated, the neighbor cells maystop using the measurement frequency specified by the configurationparameter measCycleSCell (e.g., measurement cycle for Scells indeactivated state), and may begin using a different (e.g., faster)measurement cycle. In an example, the activation of one cell may triggera scaling down of the measurement cycle frequency (e.g., a scaling downof measCycleSCell) to a smaller value. In an example, the SCeNB may senda command to the WTRU to request an aperiodic CQI measurement report besent to the MeNB (e.g., over RRC). For example the aperiodic CQImeasurement may be triggered if the SCeNB detects degradation of uplinkchannel conditions.

When one or more of the triggers for performing and/or reportingmeasurements is detected by the WTRU, the WTRU may determine to activateand/or deactivate a layer based on detecting the trigger. For example,upon determining to activate the primary layer MAC instance based ondetecting a trigger to perform or report measurements, the WTRU maymaintain the secondary MAC instance as active. In another example, uponactivating the primary layer, the WTRU may deactivate the secondarylayer. In an example, one or more of the triggers for performing and/orreporting measurements may trigger the WTRU to activate a secondarylayer. In an example, one or more of the triggers for performing and/orreporting measurements may trigger the WTRU to deactivate a secondarylayer for which the radio link quality has degraded. In an example,rather than directly activating or deactivating a given layer based ondetecting one or more of the triggers for performing and/or reportingmeasurements, the WTRU may sending an indication to the network thatindicates that the trigger has been detected. The WTRU may then wait foran explicit indication to activate an inactive layer (e.g., the primarylayer) and/or deactivate an active layer (e.g., the secondary layer).For the example, the indication to switch or activate the primary layermay be transmitted to the WTRU over the primary layer PDCCH/MAC. TheWTRU may monitor the primary layer PDCCH using the stored configurationfor a certain configured period of time after detecting one or more ofthe measurement performance/reporting triggers. If the timer expires andno indication is received, the WTRU may continue to operate with thesecondary layer as the active layer. The indication may also betransmitted over the secondary layer PDCCH/MAC or via an RRC message.

When one or more of the triggers for performing and/or reportingmeasurements is detected by the WTRU, the WTRU may initiate an RRCprocedure, for example an RRC connect re-establishment procedure. TheRRC procedure may be utilized to indicate to the network that one ormore layers are to be deactivated and/or activated. For example, uponone or more of the triggers for performing and/or reportingmeasurements, the WTRU may activate the primary MAC instance, forexample using a stored configuration. The WTRU may initiate a SchedulingRequest in the primary layer, for example using RACH (e.g., a RA-SR).Upon being schedule, the WTRU may transmit an RRC message (e.g., an RRCConnection Re-establishment Request) that may include one or more of acontext identity, a WTRU identity, and/or other information that may beutilized by the network to determine the identity of the WTRU and thecorresponding configuration for accessing the cell. The identityinformation may have been part of the configuration of the primary layeras previously received by the WTRU.

The WTRU may receive a configuration/conformation message in response tothe RRC message. For example, the configuration/conformation message mayindicate that the WTRU should reuse one or more of the security context,the C-RNTI, PHY parameters, MAC parameters, RLC parameters, PDCPparameters, etc. that were preconfigured for use in the primary layer.In an example, if the configuration/conformation message does notexplicitly provide different parameters or indicate that preconfiguredparameters should be discarded, the WTRU may assume the parametersprevious provided and stored to be valid. The configuration/conformationmessage may include additional configuration parameters that maysupplement or overwrite at least part of the stored configuration forthe primary layer. The WTRU may then perform mobility procedure(s)related to configured (e.g., active and/or suspended) DRBs such that theDRBs may be re-associated with the primary layer. If the RRC procedureis unsuccessful, the WTRU may release the stored configuration for theprimary layer and initiate a RRC Re-establishment procedure, perform aninitial access, and/or move to idle mode.

The WTRU may be configured to perform various actions upon activation ofa primary layer. For example, if the WTRU detects a trigger (e.g., suchas the triggers described for initiating measurements, measurementreporting, activation/deactivation of a layer, etc.), the WTRU maydetermine to initiate monitoring of the PDCCH of the primary layer usingthe preconfigured configuration information while continuing normaloperation in the secondary layer. In example, the WTRU may stopmonitoring the secondary layer upon determining to begin monitoring thePDCCH of the primary layer. In an example, the WTRU may wait to fullyactivate the primary layer (e.g., instead continuing with monitoring thePDCCH) until the WTRU receives an explicit PDCCH order that indicatesthat the WTRU should activate the primary layer. For example, the PDCCHorder may indicate to the WTRU that it should activate the primary layerusing the pre-configured set of resources for the primary layer. ThePDCCH order may configure the WTRU with a dedicated RACHresource/preamble to use for initial UL access in the primary layer. Inan example, the PDCCH order may correspond to a PDCCH order for a RACHprocedure. The WTRU may determine that the PDCCH order for the RACHprocedure corresponds to a trigger for the WTRU to activate the primarylayer. The PDCCH order may also be received over the secondary layer andbe used as a trigger for the WTRU to activate the primary layer.

Based on determining to activate the primary layer, the WTRU mayactivate and instantiate the MAC instance associated with the primarylayer using the preconfigured configuration information. As part of theactivation procedure, the WTRU may attempt to initiate UL access to theprimary layer. For example, the WTRU may initiate a random accessprocedure at the primary cell. One or more of the preconfiguredconfiguration information and/or a dynamic layer activation message(e.g., PDCCH order) may include one or more of a dedicated RACHpreamble/resource to use of the initial access procedure and/or adedicated C-RNTI to be used in the primary layer.

The WTRU may send an UL message to the network over the primary layer,for example as part of the initial random access procedure. The ULmessage may include one or more of a buffer status report (BSR) forbearers utilized in the previously active layer, an identification orindication of the previous layer, a PDCP status report for the bearersutilized on the previous layer, a WTRU identity (e.g., a C-RNTI of theprimary layer, some other unique WTRU ID), an RRC re-establishmentmessage (e.g., indicating reason of failure at the previous layer, andor other information), and/or some other RRC message that indicates theWTRU is requesting to switch layers and transfer bearers between layers(e.g., which may indicate the radio bearers, a buffer status report foreach bearer located in the other layer, a WTRU ID, a PDCP context andstatus report, and/or an ID of the previous layer, etc.). If the WTRUwas utilizing DRX on the primary layer, the WTRU may move to active timeor to a shorter DRX cycle and/or the WTRU may send an indication that ithas moved to active time reception. The WTRU may send an SR, and thetransmission of an SR may be an implicit indication that the WTRU is inactive time and that it is attempting to switch layers.

Upon activation of the primary layer the WTRU may maintain the secondarylayer as active or may deactivate the secondary layer. The deactivationof the secondary layer may the WTRU temporarily suspending the operationof the secondary MAC layer. While the secondary layer is deactivated,the WTRU may not perform physical layer transmission and/or reception.The WTRU may delete the secondary layer configuration upon explicitindication from the network and/or upon a handover of the secondarylayer. If the WTRU deactivates the secondary layer, it may delete theMAC instance and release the PHY resources associated with the secondarylayer. In another example, upon activation of the primary layer the WTRUmay maintain the secondary layer as active and may continue normalreception/transmission procedures on the secondary layer.

Upon activation of the primary layer, the WTRU may be configured toperform one or more bearer mobility procedures to transfer one or morebearers or data flows to a different data path (e.g., the primarylayer). For example, a set of one or more SRBs may be configured uponactivation of the primary layer and mapped to the primary MAC instance.The SRB configuration to use upon activation of the primary layer may beincluded in the pre-configured configuration information stored in theWTRU. In an example, both control plane and user plane bearers utilizedby the WTRU upon primary layer activation may be preconfigured andstored as configuration information for the primary layer at the WTRU.In an example, a subset of the RBs from the secondary layer may beswitched and re-mapped to the primary layer.

The radio bearers that were previous active in the secondary layer maybe transfer to the primary layer, may remain at the secondary layer,and/or may be released. For example, the network may be configured topreform reconfiguration and mobility operations of radio bearers fromone layer to the other. As an example, if the primary layer is activatedthe WTRU may suspend the radio bearer transmission/reception on thesecondary layer, but keep/store the bearer context for that layer forfuture use. In another example, when the primary layer is activate, theWTRU may keep the secondary layer bearers active and continuereception/transmission procedures of those bearers while alsotransmitting/receiving data on the macro layer. For example, the WTRUmay be configured to receive control plane data via the macro layer(e.g., but not user plane data) upon activation of the macro layer, ormay receive both control plane data and data plane data on the newlyactivated macro layer (e.g., as configured by the network in thepreconfiguration information). The WTRU may move a radio bearer from thesecondary layer to the primary layer upon receiving an RRCreconfiguration message over either the macro layer or over thesecondary layer. For example, the RRC reconfiguration message may bereceived as part of message 4 when the primary layer is activated and aRACH procedure is initiated.

The WTRU may perform a partial reconfiguration/radio bearer mobilitywhen initially activating the primary layer, (e.g., transfer SRBs butnot DRBs). The WTRU may perform a partial reconfiguration/radio bearermobility (e.g., transfer SRBs but not DRBs) upon an receiving explicitindication from the network (e.g., PDCCH order, MAC control, orsuccessful random access response) indicating that one or more bearersshould be transferred. The WTRU may perform a full radio bearer mobilityto the primary layer if configured to do so in the preconfigurationinformation for the primary layer.

In an example, the WTRU may autonomously initiate radio bearer mobilityfrom the secondary layer to the primary layer and delete the secondarylayer context. The autonomous mobility may be based on pre-configuredinformation and/or the WTRU may assume that the secondary layer shouldbe deactivated if the primary layer is activated unless the networkexplicitly indicates that the secondary layer is to remain active. Oncethe switching of the DRBs and/or SRBs is performed, either vianetwork-controlled or WTRU autonomous procedures, the WTRU may before anRRC procedure (e.g., RRC connection re-establishment procedure) to applyand/or confirm the RB reconfigurations.

As noted above, the WTRU may utilize a multi-data path connection for avariety of reasons. For example, multiple serving sites may be utilizedin order to achieve data throughput gains (e.g., enable inter-layeraggregation of resources available to the WTRU), allow for WRTUautonomous mobility (e.g., allowing a WTRU to determine and access cellsof various layers that may provide the highest quality connection at anygiven time instance), allow the WTRU to recover for connectivityimpairments (e.g., if the WTRU detects RLF and/or a decrease in thequality of a given layer, the WTRU may switch to another layer, forexample without having to perform a reestablishment procedure), and/orfor network controlled mobility (e.g., offloading traffic from one layerto another and/or other network management reasons). Since connectivityto different serving sites may be established for varying reasons, thetriggers and/or procedures for accessing a secondary serving site and/ordeactivated layer may be different depending on the purpose of themulti-serving site connection. For example, if access to a secondaryserving site is for the purpose of achieving data throughput gains, theWTRU may maintain a primary serving site in an activated state uponactivation of a secondary serving site. However, if the WTRU isactivating a secondary serving site for the purposes of macro layeroffload, the WTRU may deactivate the primary layer upon activating thesecondary layer. Similarly, the triggers for performing measurements,sending measurement reports, and/or activating and/or deactivating alayer may be different depending on the purpose of performingmulti-serving site operation.

As an example, consider a case where dual-site connectivity is used toachieve throughput gains for a WTRU. In this example, multiple servingsites may be used substantially simultaneously by the WTRU in order toincrease the amount of data transmitted and/or received by the WTRU. Forexample, the WTRU may be initially in an RRC_CONNECTED state with asingle layer. The WTRU may receive a reconfiguration message thatconfigures the WTRU to access one or more cells of a second layer. Thereconfiguration may activate the second layer or the reconfiguration maypreconfigure the layer for subsequent activation. For example, if thereconfiguration configures the WTRU for “dual connectivity” whileleaving one or more cells of the added layer in a deactivated state, theWTRU may receive a measurement configuration for performing measurementson cells of the deactivated layer. The preconfiguration may includeinformation indicative of the circumstances that may trigger the WTRU tosend measurement reports to the active layer and/or autonomouslyactivate the preconfigured layer. For example, based on detecting atrigger received in the received configuration and/or some implicitlydetermined trigger, the WTRU may initiate one or more procedures toreport quality measurements to the network (e.g., activated layer) sothat the active serving site (e.g., RRC entity) may subsequentlyreconfigure (e.g., by RRC) and/or activate (e.g., by MAC CE) one or morecells of a deactivated layer. In an example, rather than or in additionto being triggered to send the measurement report, the WTRU may beconfigured to autonomously activate one or more cells of an deactivatedlayer based on detecting the one or more triggers indicated in thereconfiguration and/or implicitly determined. For example, the WTRU mayinitiate a RACH procedure in a cell to be activated in order to notifythe network of the activation, obtain uplink timing alignment, obtaindedicated resources (e.g., request scheduling), and/or establish aconfiguration for accessing the cell. The WTRU may maintain both layersas active substantially simultaneously in order to increase overall datathroughput.

In an example, the WTRU may be configured to access multiple layers aspart of WTRU-autonomous mobility. For example, if the secondary servingsites correspond to SCeNBs, the coverage area of the secondary servingsites may be relatively small (e.g., as compared to a MeNB). However,SCeNBs may be deployed in clusters, such that multiple SCeNBs may beaccessible by a WTRU in a relatively small area. In this case, the WTRUmay be configured to monitor the various SCeNBs in order to determinewhich serving site may provide the highest quality access to the WTRU ata given point in time. Since the coverage area of the cells for theseserving sites may be relatively limited, the WTRU may move into and/orout of coverage areas more frequently than in macro cell deployments.Therefore, rather than relying solely on network controlled mobility(e.g., network controlled handover, network controlled layer activation,etc.), the WTRU may be configured to perform some autonomous mobilityprocedures. For example, the WTRU may be configured to autonomouslyswitch from a first (e.g., small cell) layer to a second (e.g., smallcell) layer, activate a deactivated (e.g., small cell) layer,deactivated an activated (e.g., small cell) layer, and/or the like.

For example, the WTRU may be initially in an RRC_CONNECTED state whileaccessing one or more layers. The WTRU may receive and/or may havepreviously received a reconfiguration message that configured the WTRUto access one or more cells of a layer that are not currently active.For example, the WTRU may be connected to a primary layer associatedwith a MeNB and a first secondary layer associated with a first SCeNB.The WTRU may have preconfigurations for a plurality of other secondaryserving sites associated with other SCeNBs. The WTRU may be configuredwith a measurement configuration for performing measurements on cells ofthe one or more deactivated layers. The preconfiguration may includeinformation indicative of the circumstances that may trigger the WTRU toautonomously activate a preconfigured layer and/or deactivate acurrently active layer. For example, based on detecting a criteria thatindicates a deactivated small cell layer is of higher quality than thecurrent small cell layer (e.g., cell quality of the deactivated layer isgreater than that of the activated layer by an offset and/orpredetermined threshold), the WTRU may be configured to autonomouslyactivate one or more cells of an deactivated layer based and/ordeactivate the currently connected small cell layer. As an example, thesmall cells may be part of a small cell cluster, and the WTRU may beauthorized by the network to perform autonomous mobility between smallcells within the cluster. The WTRU may initiate a RACH procedure in acell to be activated in order to notify the network of the activation,obtain uplink timing alignment, obtain dedicated resources (e.g.,request scheduling), and/or establish a configuration for accessing thecell.

In an example, the WTRU may be configured to access multiple layers inorder to maintain connectivity during periods in which one or morelayers are experience poor radio quality. For example, the WTRU may beconfigured to perform some form of WTRU-autonomous mobility in order toavoid radio link failure in a given layer from preventing the WTRU fromcommunicating with the network or otherwise maintain its connection withthe network. For example, the WTRU may determine that a cell (e.g.,PCell) failure in an active layer (e.g., the WTRU detects radio linkproblems; WTRU determines UL RLF and/or DL RLF; a measured signalquality falls below a threshold, etc.) has deteriorated, the WTRU maytake one or more actions in another layer to maintain sessioncontinuity. For example, the WTRU may be initially in an RRC_CONNECTEDstate while accessing one or more layers. The WTRU may receive and/ormay have previously received a reconfiguration message that configuredthe WTRU to access one or more cells of a layer that are not currentlyactive. The WTRU may have preconfigurations for a plurality of otherserving sites which it may be configured to activate autonomously. TheWTRU may perform RLM on one or more cells (e.g., the PCell) of theactive layer(s). The UE may determine that it is experiencing animpairment (e.g., loss of connectivity to the concerned cell) such asone or more of radio link problems, out-of-synch conditions, UL RLF, DLRLF, and/or the like. Based on detecting the adverse channel conditions,the WTRU may initiate a procedure to autonomously activate one (or morecells) of the primary layer (e.g., if previously deactivated) and/orsome other deactivated later and initiate a RACH procedure to notify thenetwork of the failure of the other layer, to obtain UL timing alignmentof the primary layer, to obtain dedicated resources in the primarylayer, to obtain a configuration of such resources; and/or to initiate areconfiguration procedure for the layer associated with the failure. TheWTRU may receive a RRC reconfiguration with or without mobility controlinformation (e.g., a reconfiguration or a HO command) from the primarylayer (e.g., layer associated with RRC entity) that reconfiguresresources mapped to the failed layer. For example, the resources may bemoved to the primary layer and/or a different secondary layer.

In an example, the WTRU may be configured to access multiple layers inorder to support network controlled mobility across a plurality oflayers. For example, the WTRU may be configured to inform the networkwhen it detect a new layer (e.g., based on measurements) such that aserving site may perform network-controlled connectivity management. Forexample, the WTRU may be initially in an RRC_CONNECTED state with asingle layer. The WTRU may receive a reconfiguration message thatconfigures the WTRU to access one or more cells of a second layer. Thereconfiguration may activate the second layer or the reconfiguration maypreconfigure the layer for subsequent activation. For example, if thereconfiguration configures the WTRU for “dual connectivity” whileleaving one or more cells of the added layer in a deactivated state, theWTRU may receive a measurement configuration for performing measurementson cells of the deactivated layer. The received measurementconfiguration may indicate criteria for determining whether or not acell should be considered available and/or suitable. If a cell meets thecriteria, the WTRU may be configured to report the measurements of thecells of that layer. The network may use the reported measurements totrigger WTRU mobility, for example, by sending an RRC reconfigurationwith or without mobility control information (e.g., a reconfigurationand/or a HO command) that indicates that the WTRU should begin accessinga cell.

The WTRU may be configured to perform mobility procedures for one ormore serving cells of a serving site. For example, a serving cell of asecondary serving site may be subject to different mobility proceduresthan that of a serving cell of a primary serving site, for example ifthe RRC entity at the network side is located at the primary servingsite. In an example, mobility procedures for one or more RBs (e.g., DRB,SRB, etc.) may be performed such that the RBs are moved from a firstserving site to a second serving site. As an example use case, an RB maybe mapped to a first secondary serving site, and the WTRU may move suchthat it may find better coverage at a different secondary serving site(e.g., a serving site served by a different SCeNB). Methods and systemsare disclosed for user-plane and/or control-plane mobility when the WTRUmoves one or more bearers mapped to a first secondary serving site to adifferent secondary serving site (e.g., while maintaining a constantconnection to a primary serving site served by a MeNB).

As an example of possible architectures where RB mobility betweenserving sites may be beneficial, consider the case where the PDCPinstance and the RLC instance at the network side may be located in thein primary serving site (e.g., there may be no PDCP instance in thesecondary serving site and/or no RLC instance in the secondary servingsite). In such a scenario, for a given RB the DL-SCH and/or the UL-SCHmay be available in both a primary serving site and a secondary servingsite (e.g., which may be referred to as a pooled RB) and/or the DL-SCHand/or UL-SCH may be available for transmission associated with asecondary serving site, but not for a primary serving site (e.g.,although other scenarios for RB mappings may also be applicable). Inanother example, the PDCP instance at the network side may be located inthe in primary serving site (e.g., there may be no PDCP instance in thesecondary serving site), but there may be RLC instance at each of theprimary serving site and the secondary serving site. Similarly, theremay be respective PDCP instances and RLC instances at each of theprimary serving site and the secondary serving site. In either case,there may be scenarios or configurations where for a given RB the DL-SCHand/or the UL-SCH may be available in a secondary serving site, but nota primary serving site. There may be other architectures where for agiven RB, transmission to the primary serving site may be unavailable.

Since it is envisioned that for at least some types of SCeNBs thecoverage area may be relatively limited (e.g., a smaller coverage areathan a MeNB), a mobile WTRU may move into and/or out of coverage of oneor more serving cells for the secondary serving sites. In such a case,handover procedures may be defined in order to move one or more bearersbetween SCeNBs and/or between an SCeNB and an MeNB. These handovers maynot be true WTRU handovers (e.g., where an entire WTRU context may betransferred from a first serving site to a second serving site), as theRRC connection may be unchanged, for example in the case of centralizedcontrol entity (e.g., and/or the primary RRC connection may be unchangedin the case of coordinated control entities or distributed controlentities). Methods and systems are disclosed for control of mobilitychanges for RBs mapped to SCeNBs when the RRC connection to theRCNC/MeNB may be unchanged. As an example, SCeNB mobility (e.g.,mobility of one or more RBs from a first secondary serving site to asecond secondary serving site) may be described as “user plane mobility”and/or “data radio bearer handovers.”

For example, in order to support SCeNB mobility, the WTRU may beconfigured to measure and/or detect one or more target cells. The WTRUmay be configured by the network and/or autonomously control thehandover between a source cell at a first serving site and a target cellat a second serving site. The WTRU may be configured to manage the flowof UL and DL data in order to support lossless operation andminimize/eliminate duplication of transmitted data.

For example, a primary serving site (e.g., a serving site associatedwith a MeNB and/or a serving site in which the RRC instance/primary RRCinstance is maintained at the network side), may be configured tocontrol bearer and/or connection mobility for secondary serving sites.For example, if a centralized control architecture is utilized, theprimary serving site may be configured to control RB mobility at one ormore secondary serving sites using the RRC connection for the WTRU. TheRCNC and/or MeNB may be configured to coordinate secondary serving sitemobility with the WTRU, the source secondary serving site, and/or thetarget secondary serving site.

For example, the primary serving site (e.g., the RCNC and/or MeNB) maybe configured to trigger SCeNB mobility based on measurement eventsreported to the primary serving site. The WTRU may be configured by theRCNC and/or MeNB to detect and report on measurement events as describedherein. For example, a WTRU may be configured to compare the quality ofpotential SCeNB small cells and/or the MeNB macro cell with SCeNB smallcells that it is currently accessing.

In an example, the primary serving site (e.g., the RCNC and/or MeNB) maybe configured to trigger SCeNB mobility based on CQI reporting from theWTRU and/or SRS reception quality relayed from SCeNBs to the MeNB. TheWTRU may be configured to report CQI to the primary serving site and/orthe secondary serving site. The WTRU may transmit SRS for multiple smallcells, for example including one or more cells that the WTRU may not becurrently actively transmitting to and/or receiving from.

In an example, SCeNB mobility in the WTRU may be initiated by an RRCreconfiguration procedure triggered by the RCNC and/or MeNB. The RRCreconfiguration procedure may include the MeNB sending signaling to theWTRU that includes one or more information elements that indicate thatthe WTRU is to perform a limited mobility procedure for certain DRBswithout modifying the WTRU connection to the primary serving site (e.g.,indicate the reconfiguration is for SCeNB mobility). For example, one ormore data flows (e.g., DRBs) may be rerouted to from a secondary servingcell associated with a first secondary serving site to a differentsecondary serving cell associated with a second secondary serving site.The amount and type of information included in the reconfigurationmessage may depend on how the data paths are split within the network(e.g., above RLC, above PDCP, etc.). For example, the reconfigurationmessage may explicitly indicate one or more of the identity of one ormore radio bearers to be moved, a SAP identity of the target servingsite, transmission and reception sequence numbers for RBs being moved,etc. The reconfiguration messaging may indicate access information infor accessing the target cell at the new secondary serving site. Forexample, the access information may include a dedicated random accessconfiguration and/or other system information of the target cell. In anexample, the WTRU may already have one or more bearers mapped to thetarget serving site, and the reconfiguration procedure may be to moveadditional bearers from another serving site to the target serving site.

The primary serving site (e.g., RCNC and/or MeNB) may preconfigure theWTRU with configuration information for one or more potential targetsecondary serving sites (e.g., SCeNBs). Since the WTRU may bepreconfigured with access information for potential target cellsassociated with different secondary serving sites (e.g., SCeNBs), themobility procedure may be performed with using RRC signaling proceduresin order to configure and execute the handover. For example, WTRU cellswitching may be performed by enabling and/or disabling (e.g.,activating and/or deactivating) cells associated with one or moreSCeNBs. For example, MAC control signaling (e.g., MAC CE) may be used toinitiate cell switching between a plurality of preconfigured secondaryserving site cells. Further, although examples may be described formobility between secondary serving sites, the methods and systemsdisclosed may be equally applicable to switching data flows between oneor more secondary serving sites (e.g., SCeNBs) and a primary servingsite (e.g., MeNB).

In an example, a secondary serving site may trigger data flow mobilityand/or may assist the primary serving site in performing data flowmobility. For example, if a coordinated control architecture and/ordistributed control architecture are utilized, some RRC connectionfunctionality may be control at the secondary serving site. In suchscenarios, secondary serving sites (e.g., SCeNBs) may be configured totrigger and/or control secondary serving site (e.g., SCeNB) mobilityand/or may assist the primary serving site (e.g., MeNB) with secondaryserving sites (e.g., SCeNBs) mobility. For example, in a coordinatedcontrol architecture and/or in a distributed control architecture one ormore SRBs may be managed by the secondary serving site such that thesecondary serving sites (e.g., SCeNBs) may be configured with a directcontrol signaling path to the WTRU. The secondary serving site mayutilize the control path to send control signaling (e.g., MAC controlsignaling) that may be used for SCeNB mobility purposes (e.g., secondaryserving site activation and/or deactivation).

Secondary serving sites (e.g., SCeNBs) may configure measurement eventsand receive measurement reports from a WTRU. The WTRU may be configuredby a secondary serving site to detect and report on measurement events.For example, a WTRU may be configured to compare the quality ofpotential SCeNB small cells and/or the MeNB macro cell with SCeNB smallcells that it is currently accessing.

If the secondary serving site has determined to trigger secondaryserving site mobility based on RRC measurement reports and/or otherinformation (e.g., resource utilization, traffic balancing, etc.), thenthe secondary serving site (e.g., SCeNB) may send an RRC reconfigurationmessage to WTRU in order to instruct the WTRU to handover one or moredata flows (e.g., DRBs and/or SRBs) to a target cell associated withanother secondary serving site (e.g., SCeNB). In an example, thesecondary serving site (e.g., SCeNB) may inform the primary serving site(e.g., MeNB) of the desired mobility procedure (e.g., over the X2bisinterface) and the primary serving site may perform the reconfigurationprocedure that triggers the secondary serving site mobility.

Methods and systems may be defined for handling data for data flows thatundergo a secondary serving site mobility procedure. For example, if aWTRU performs a “secondary serving site handover” between cellsassociated with different secondary serving sites (e.g., SCeNBs) orbetween a primary serving site (e.g., a MeNB) and a secondary servingsite (SCeNB), the WTRU may be configured to manage UL and DL datatransmission such that data associated with a data flow being moved isproperly handled so as to avoid data loss and/or minimize/eliminateduplication of transmitted data. The technique(s) utilized to minimizethe adverse effects of secondary serving site mobility on transferreddata flow(s) may be dependent on the layer 2 split between the primaryserving site (e.g., RCNC and/or MeNB) and secondary serving site (e.g.,SCeNB). For example, the different techniques for avoiding data lossand/or minimizing data duplication/retransmission may depend on whetherthe protocol stack for the data floes is split above the MAC, above theRLC, or above the PDCP. For example, if the split is above PDCP, then X2and PDCP eNB mobility handover related procedures may be used. If thesplit is above RLC and/or above MAC, one or more additional techniquesmay be utilized to transfer data and coordinate UL and/or DLtransmission in the target cell.

If the layer 2 split is above RLC and/or above MAC, then SDUstransferred between the primary serving site (e.g., RCNC and/or MeNB)and the SCeNB may be identified by unique sequence numbers. The use ofunique sequence numbers for SDUs transferred between the primary andsecondary serving sites may avoid data loss and maintain the propersequence of transmission in the DL and/or UL. For example, if the layer2 split is above RLC, then PDCP PDU sequence numbers may be used. If thelayer 2 split is above MAC, then RLC sequence numbers may be used.Sequence numbers may be assigned to SDUs transmitted over the X2bisinterface.

Methods that may be used to handle transmission during SCeNB mobilitymay be integrated with flow control handling for secondary serving siteDL transmission. For example, a DL flow control implementation may beused to minimize data buffered in the secondary serving site (e.g.,SCeNB), for example, so that data sent and returned over the X2bis maybe minimized. For example, a window based transmission scheme and/orcredit based transmission scheme may be used in order to identifytransmitted data packets. The window based transmission scheme and/orcredit based transmission scheme may be reused upon secondary servingsite mobility in order to identify data that has and has not beensuccessfully acknowledged by the WTRU.

If secondary serving site mobility event occurs, then unacknowledgeddata may be forwarded to the target secondary serving site (e.g.,SCeNB). The source secondary serving site (e.g., SCeNB) may forwardunacknowledged SDUs to the target secondary serving site (e.g., SCeNB)and/or indicate to primary serving site (e.g., RCNC and/or MeNB) theunacknowledged sequence numbers and/or last in sequence deliveredsequence number so that primary serving site (e.g., RCNC and/or MeNB)may forward the proper SDUs to the target secondary serving site (e.g.,SCeNB).

If layer 2 is split above RLC and secondary serving site mobility istriggered, then, in the DL sufficient PDCP PDUs may be pre-generated inorder to avoid limiting DL scheduling by the secondary serving sites(e.g., SCeNB). The DL PDCP entity in primary serving site (e.g., RCNCand/or MeNB) may be unaware of the transmission status of these PDCPPDUs. The primary serving site may be configured to determine thetransmission status of the PDCP PDUs to reduce transmission latencyduring the secondary serving site mobility event.

For example, the secondary serving site (e.g., SCeNB) may return DL RLCSDUs to primary serving site (e.g., RCNC and/or MeNB) that have not beenacknowledged at the RLC layer by the WTRU. Sequence numbers of RLC SDUsnot successfully received and/or the sequence number of last in-sequencedelivered RLC SDU may be indicated to the primary serving site. Thesequence numbers may indicate transmission status when secondary servingsite (e.g., SCeNB) mobility occurs.

Indicating RLC SDU sequence numbers may performed when the secondaryserving site (e.g., SCeNB) indicates RLC SDUs that have beenacknowledged by the peer RLC entity to the primary serving site (e.g.,RCNC and/or MeNB), which may maintain DL data buffering in for RLC(e.g., in the RCNC and/or MeNB). Methods such as window based transferprotocol, a credit based implementation, and/or the like may be used tocontrol the flow of RLC SDUs. The primary serving site (e.g., RCNCand/or MeNB) may be aware of the delivery status of RLC SDUs. Thedelivery status of RLC SDUs may be used upon secondary serving site(e.g., SCeNB) mobility to coordinate DL data delivery to the targetsecondary serving site (e.g., SCeNB). The sequence numbers indicated maybe the PDCP sequence number or other sequence numbers used to controlthe flow of data between the primary serving site (e.g., RCNC and/orMeNB) and the secondary serving site (e.g., SCeNB).

For UL data handling in the network, the secondary serving site (e.g.,SCeNB) may forwards in-sequence received RLC SDUs to the primary servingsite (e.g., RCNC and/or MeNB) (e.g., may forward automatically). Thesecondary serving site (e.g., SCeNB) may forward non-sequential RLC SDUsupon secondary serving site (e.g., SCeNB) mobility.

UL data handling in the WTRU may be similar to DL data handling in thenetwork. RLC SDUs that have not been successfully acknowledged may beindicated to PDCP. This may be combined with providing indications ofsuccessful RLC transmission of RLC SDUs to PDCP.

As noted above, although the procedures for secondary serving sitemobility may have been described herein for mobility between SCeNBs, themethods may be used for mobility between SCeNBs and the MeNB.

In an example, secondary serving site (e.g., SCeNB) mobility may beperformed with a Layer 2 split above MAC. If secondary serving site(e.g., SCeNB) mobility is triggered, then outstanding data alreadyprovided to the secondary serving site (e.g., SCeNB) may be handled bythe RLC instances within the primary serving site (e.g., RCNC and/orMeNB). In the DL, enough RLC PDUs may be pre-generated to avoid limitingDL scheduling by the secondary serving sites (e.g., SCeNBs). The DL RLCentity in the primary serving site (e.g., RCNC and/or MeNB) may beunaware of the transmission status of the RLC PDUs. Methods may be usedto determine the transmission status to reduce transmission latency.

Upon secondary serving site (e.g., SCeNB) mobility, the secondaryserving site (e.g., SCeNB) may identify the transmission status ofoutstanding RLC PDUs buffered in the secondary serving site (e.g.,SCeNB) and/or the last transmitted MAC SDU for a supported RLC instance.The transmission status may be which MAC SDUs have been processed andtransmitted by MAC and/or which MAC SDUs have been HARQ acknowledged bythe WTRU.

Methods may be used to combine indicating the transmission status of MACSDUs with transferring of MAC SDUs between the primary serving site(e.g., RCNC and/or MeNB) and the secondary serving site (e.g., SCeNB).For example, the secondary serving site (e.g., SCeNB) may maintainenough buffered MAC SDUs to avoid restricting DL scheduling. The primaryserving site (e.g., RCNC and/or MeNB) may limit the amount ofpre-generated RLC PDUs. The flow of MAC SDUs between the RCNC and thesecondary serving site (e.g., SCeNB) may be controlled, for exampleusing a window based transfer protocol and/or a credit based scheme.

MAC SDUs may be identified to the primary serving site (e.g., RCNCand/or MeNB) by their RLC sequence number and/or other sequence numbersused to control the flow of data between the primary serving site (e.g.,RCNC and/or MeNB) and the secondary serving site (e.g., SCeNB). The WTRUmay generate a status report for each re-routed RLC AM instance that istransfer due to secondary serving site (e.g., SCeNB) mobility, forexample, upon MAC initialization in the target cell. For RLC UM, theprimary serving site (e.g., RCNC and/or MeNB) may use the sequencenumber indication described herein to determine where to start DLtransmission in the target secondary serving site (e.g., SCeNB).

For RLC AM, a RLC status report in the target cell may be used todetermine where transmissions should start in the target cell (e.g., forUL data handling). This status report may be generated (e.g.,automatically generated) by the primary serving site (e.g., RCNC and/orMeNB) upon secondary serving site (e.g., SCeNB) mobility completion. ForRLC UM, the WTRU may be aware of where transmissions stopped in thesource secondary serving site (e.g., SCeNB) cell and may resumetransmissions from that point in the secondary serving site (e.g.,SCeNB) target cell. The WTRU may utilize HARQ feedback in the sourcesecondary serving site (e.g., SCeNB) cell to better approximate where toinitiate UL transmissions.

To support multi-scheduler principles, RLF and re-establishmentprocedures may be implemented in the primary and/or secondary servingsites during periods of adverse channel conditions. For example, a WTRUmay have one or more DRBs/SRBs that are associated with a single MACinstance. If RLM is configured for a secondary MAC instance (e.g.,associated with a SCeNB), then the WTRU may determine that RLF hasoccurred one or more serving cells (e.g., a PCell, all serving cells,etc.) configured for the MAC instance. Upon determining RLF hasoccurred, the WTRU may transmit uplink control signaling (e.g., RRC)using a MAC instance (e.g., the primary MAC instance associated with theMeNB) for which RLF has not occurred. The RRC signaling may include aRRC Connection Re-establishment request (or similar) and may be sentover SRB1 and/or over a data path corresponding to a primary MACinstance. The re-establishment request may indicate that there-establishment is not be for the primary MAC instance even though thetransmission was sent over the primary MAC instance. For example, there-establishment request may include an indication of the MAC instancethat failed and/or may be sent over SRB3. The WTRU may suspend concernedDRBs/SRBs (e.g., DRB(s) and/or SRB3 that are mapped to the secondary MACinstance that failed). The WTRU may reset the failed MAC instance. TheWTRU may release a PCell and/or SCells of the MAC instance that failed.The WTRU may re-establish PDCP and/or RLC for one or more of thesuspended DRBs when it receives a RRC Connection Reconfiguration messagethat re-associates one or more of the concerned RB(s) with a MACinstance (e.g., the previous MAC instance and/or a new MAC instance).The WTRU may resume a one or more suspended DRBs. The WTRU may resume asuspended SRB, for example, if the RBs are re-associated with thesecondary MAC instance.

For DRB mobility, a WTRU may have one or more DRBs/SRBs that areassociated with a single MAC instance. The WTRU may receive a RRCConnection Reconfiguration that reconfigures the WTRU such that one ormore of the serving cells of a given MAC instance may be removed. TheWTRU may reset the concerned MAC instance. The WTRU may suspend theconcerned DRBs and SRBs (e.g., if any), until it receives controlsignaling that re-associates one or more of the concerned RB(s) with aMAC instance. The WTRU may re-establish PDCP for the concerned DRBs andSRBs (e.g., if any). The WTRU may re-establish RLC for the concernedDRBs and SRBs (e.g., if any).

Measurement reporting may be performed across the cells of variouslayers, and measurements of cells in a given layer may be reported overone or more cells of other layers. To assist the WTRU to perform and/orrepot measurements, a small cell (e.g., a SCeNB) may be configured suchthat synchronization signals and reference signals broadcast in thesmall cells may differ from signals used for the purpose of detectionand measurement of macro cells (e.g., Primary Synchronization Signal(PSS)/Secondary Synchronization Signal (SSS), cell-specific referencesignals, etc.). For example, synchronization signals and/or referencesignals may be defined for broadcasts from small cells. A WTRU may beconfigured to detect and/or measure cells that support the newly definedsynchronization and reference signals. For example, the WTRU maydetermine that a cell is a small cell based on detecting synchronizationsignals and/or reference signals that are associated with small celloperation.

For example, when the WTRU receives a measurement configuration the WTRUmay be notified that synchronization signals and/or reference signalsthat are associated with small cell operation may be present in a givenfrequency and/or are to be measured as a certain measurement object. Themeasurement configuration may indicate to the WTRU whether legacy typesof signals may be present at the indicated frequency. The measurementconfiguration may include additional information that assists the WTRUin detecting synchronization signals and/or reference signals that areassociated with small cell operation. For example, the measurementconfiguration may indicate one or more periods of time when thesynchronization signals and/or reference signals that are associatedwith small cell operation may be transmitted/received and/or one or moreproperties of the synchronization signals and/or reference signals thatare associated with small cell operation.

For example, the measurement configuration may indicate a period of timeduring which synchronization signals and/or reference signals that areassociated with small cell operation may be transmitted/received. Theindication regarding the timing of the synchronization signal and/orreference signal transmission may be as a function of frame numberand/or subframe number. For example, the frame number and/or subframenumber may correspond to frames/subframes of the primary layer.Transmission of the synchronization signals and/or reference signalsthat are associated with small cell operation may occur as pattern ofsubframes that repeat periodically. For example, the configurationinformation may indicate the frequency at which the pattern is repeated.

In an example, the measurement configuration may indicate one or moreproperties for one or more synchronization signals and/or referencesignals that are associated with small cell operation. For example, themeasurement configuration may indicate an index and/or identifier thatis used for the generation of a synchronization signal and/or referencesignal that is associated with small cell operation (e.g., such as azadoff-chu base sequence index). In an example, the measurementconfiguration may include an indication of the type of cell and/or thetype of signal the WTRU may expect to find at the configured frequency.For example, the type of cell and/or the type of signal may be used asan indication of one or more of the type of access technology associatedwith the cell, the sustained data rates achievable in the cell, thecurrent state of the cell (e.g., congested, accessible, etc.), and/orthe like. The type of cell and/or the index used to generate asynchronization signal and/or reference signal that is associated withsmall cell operation may be indicative of one or more conditions thatthe WTRU should meet in order to operate or use the resources of thecell. For example, the type of cell and/or the index used to generate asynchronization signal and/or reference signal that is associated withsmall cell operation may indicate one or more of a capability thatshould be present in order to access the cell, a maximum speed that theWTRU may operate in while in the cell, information related to the rateof change of the channel conditions in the cell, and/or the like.

The WTRU may report measurement the results of measurements performed onone or more detected small cell(s) that transmit synchronization signalsand/or reference signals that are associated with small cell operation.For example, the WTRU may report measurements performed on a small cellafter detecting a cell that broadcasts synchronization signals and/orreference signals that are associated with small cell operation. TheWTRU may be configured to report measurements of a small cell and/ormeasurement information of synchronization signals and/or referencesignals that are associated with small cell operation based on detectinga trigger such as the received power or quality being above a giventhreshold. In an example, even if the WTRU detects a configured triggerfor reporting measurements related to small cell operation, the WTRU mayrefrain from reporting the measurements if the WTRU does not meet one ormore conditions for operating or using the resources of the cell. Forexample, the synchronization signals and/or reference signals that areassociated with small cell operation may indicate one or morecapabilities that the WTRU should possess in order to operate in thecell. The WTRU may report measurements for a cell if the WTRU detects ameasurement reporting trigger and the WTRU meets the criteria foraccessing the cell.

The WTRU may include one or more items of information regarding thesmall cell in the measurement report. For example, the measurementreport may include one or more of an identifier of the signal beingmeasured, an identifier of the cell being measured, an indication of thetype of signal measured, an indication of the type of cell measured, anindication of a property of the signal detected, and indication of aproperty of the cell detected, and/or the like. The measurement reportmay indicate whether the detected/measured signal is of a legacy type ora synchronization signal and/or reference signal that is associated withsmall cell operation. The measurement report may include informationindicating whether the WTRU may operate in the detected cell. Otherinformation that may be included in the measurement report may compriseone or more of measurement results regarding the rate of change of thechannel, a mobility state of the WTRU, a number of recent mobilityevents experience by the WTRU with a given time period (e.g., such asnumber of reconfiguration procedures with mobility, number ofre-establishment procedures, etc.), and/or the like.

Mobility state estimation (MSE) may be performed by the WTRU. Forexample, as part of the MSE procedures, the WTRU may determine/count thenumber of handovers (e.g., and/or cell reselections) performed by theWTRU within a period of time. Based on the number of handovers (e.g.,and/or cell reselections) performed within the time period, the WTRU maydetermine a mobility state for itself. For example, the WTRU maydetermine that it is operating in a low, medium, or high mobility state.The state determined in the MSE may be used to scale one or moremobility variables, such as the Treselection timer. For example, thevalue of the Treselection timer may be scaled to a larger value for lessmobile WTRUs and may be scaled to a shorter value for more mobile WTRUs.

Independent mobility states may be associated with the primary andsecondary layers. For example, the primary layer may be associated witha first mobility state for the WTRU and the secondary layer may beassociated with a second mobility state for the WTRU if the WTRU isoperating using dual connectivity. For example, the MSE in each layermay be determined by separately counting the number of reconfigurationsinvolving mobility in each layer. The WTRU may maintain independent MSEvalues and/or perform independent determinations regarding the MSE foreach configured layer. The WTRU may be configured to scale one or moreparameters associated with a given layer based on the MSE determinedindependently for that layer. For example, one or more configuredhandover parameters (e.g., time-to-trigger (TTT)) for a given layer maybe scaled based on the MSE determination for that layer. Eventsassociated with one or more measurement objects corresponding to a givenlayer may be scaled according to the MSE for that layer. In an example,the WTRU may measure events associated with the PCell of a layer whendetermining MSE information for that layer, but may refrain fromconsidering SCell(s) for that layer when determining the MSE for thelayer.

In an example, the WTRU may also count other mobility-related events inorder to determine MSE information, for example on a per layer basis.For example, for a given primary and/or for a secondary layer, the WTRUmay maintain count(s) of one or more of the number of DL radio linkfailures, the number of UL radio link failures, the number of MACreconfigurations for a secondary layer, the number of unique cellsdiscovered for a given layer, whether the WTRU has detected radioconditions that are above a specified threshold for more than aspecified period of time for a cell of a secondary layer, and/or thelike. The counts may be used by the WTRU to determine MSE informationfor a layer. The amount of time over which the counts are measured forMSE may be a function of the characteristics of a cell (e.g., cell size,etc.).

A WTRU may be configured to perform one or more autonomous mobilityprocedures. For example, a WTRU may be configured for operation within aplurality of serving cells associated with a secondary layer. One ormore cells configured for use by the WTRU within the secondary layer maybe in a deactivated state. The WTRU may be configured to performmeasurements of the cells within the secondary layer (e.g., activatedand/or deactivated cells). Such measurements of active and/ordeactivated cells within a secondary layer ay trigger the WTRU toperform one or more autonomous mobility events. As an example, the WTRUmay be triggered to begin performing measurements for the purpose ofautonomous mobility based on WTRU transmission buffer information. Forexample, if one or more buffers include an amount of data that isgreater than a predetermined threshold, then the WTRU may beginperforming measurements for the purpose of autonomous mobility.

For example, the WTRU may determine that one or more measured qualitiesassociated with a deactivated cell of a secondary layer has becomebetter than one or more measure qualities of an activated cell of thesecondary layer, for example by more than a configured offset value.Rather than or in addition to comparing measurements between anactivated cell of the secondary layer and a deactivated cell of thesecondary layer (e.g., with an offset value), WTRU may comparemeasurements of a deactivated cell of the secondary layer to a thresholdvalue in order to perform autonomous mobility. For example, the WTRU maydetermine that measurements associated with a deactivated cell of asecondary layer have become better/greater than a threshold value.

If the measured quality of the deactivated cell exceeds the measuredquality of the activated cell (e.g., by more than an offset value)and/or the measured quality of the deactivated cell exceeds a threshold,the WTRU may be configured to initiate a procedure to establish aphysical layer connection to the deactivated cell (e.g., the WTRU mayattempt to connect to and/or activate the cell in the WTRU secondarylayer configuration). Such a procedure may include a procedure to movethe deactivated cell from a dormant mode to an active mode. For example,the WTRU may initiate a procedure access and/or create a connection tothe previously deactivated cell. Such procedure may be similar to aconnection establishment procedure. For example, the UE may perform aRACH procedure on uplink resources of the previously deactive cell. TheRACH procedure may be performed using dedicated PRACH signaling. Forexample, the dedicated RACH parameters may enable the eNB serving thecell the WTRU is attempting to access to uniquely identify the WTRU.Rather than or in addition to attempting to access the cell via RACH,the WTRU may transmit RRC signaling to the concerned eNB. Once the RACHand/or RRC procedures successfully complete(s), the WTRU may move thecell and consider it to be in an activated state. In an example, theWTRU may move its previous cell (e.g., of the secondary layer) to adeactivated state, for example if the previous cell is no longer ofsufficient quality. In an example, the WTRU may transmit controlsignaling to notify the MeNB of the WTRU autonomous activation of thecell in the secondary layer. The WTRU may also indicate deactivation ofits previous cell in the secondary layer, if applicable. The MeNB maycoordinate with the corresponding SCeNB(s) for proper routing of packetsand other information related to the WTRU dual connectivity.

A WTRU may be configured to configure/reconfigure one or more radiobearers based on reception of reconfiguration signaling (e.g., thereconfiguration signaling may be or may not be mobility related). Forexample, upon reception of an RRCConnectionReconfiguration message, theWTRU may perform various actions related to RBs associated with aprimary and/or secondary radio bearer. For example, if thereconfiguration message indicates the addition of at least one SRB for asecondary layer (e.g., SRB0, SRB1, and/or SRB2 in the case of acoordinated control plane, SRB3 in case of a distributed control plane,may not applicable to the centralized control plane, etc.) the WTRU maybe configured to perform various actions based on its currentconnectivity. For example, if the WTRU has a single RRC Connection andthe RRC connection is with the primary layer (e.g., as in a distributedcontrol plane), the WTRU may implicitly determine that the identity forthe SRB to be added in the secondary layer is SRB3 (e.g., INTEGER(3))independently of the value of the srb-Identity in the reconfigurationmessage (e.g., if present).

If the SRB being added is the first SRB for the secondary layer and ifthe secondary layer implements a separate security context for thecontrol plane, then the WTRU may configure lower layers (e.g., PDCP)according to the integrity protection algorithm and the Krrint keyderived for and applicable to the secondary layer and/or may configurelower layers (e.g., PDCP) according to the ciphering algorithm and theKupenc, Krrcenc keys derived for and applicable to the secondary layer.The WTRU may consider that security to be inactive (e.g., not started)until successful completion of the Security Mode Activation procedurefor the secondary layer. If the SRB being added is the first SRB for thesecondary layer, and if the secondary layer implements a securitycontext that is common with the macro layer for the control plane(and/or with any other layer for which security already is activated),the WTRU may apply the security context (e.g. keys) of the macro layer(e.g., or other layer with shared security) to the secondary layer andconsider security as started for the secondary layer. The WTRU mayassociate the newly added SRB to the MAC instance for the secondarylayer. For example, control plane data for the corresponding bearer maybe transmitted using a logical channel associated with the correspondingMAC instance.

If a received reconfiguration message indicates the addition of at leastone DRB for a secondary layer and/or if the reconfiguration messageindicates that at least one DRB is moved from a first layer (e.g., aprimary layer) to a second layer (e.g., a secondary layer) or viceversa, then the WTRU may perform various actions to add or move thebearer configuration to a given layer. For example, if the secondarylayer implements a security context that is common with the macro layerfor the user plane (and/or with another layer which security is alreadyactivated for), the WTRU apply a new value for the drb-identity. If thesecondary layer implements a security context that is common with themacro layer for the user plane (and/or with another layer which securityis already activated for), the WTRU may configure lower layers (e.g.,PDCP) according to the ciphering algorithm and the Kupenc key applicableto the macro layer (e.g., or other layer with shared security). If thesecondary layer implements a separate security context for the userplane, the WTRU may configure lower layers (e.g., PDCP) according to theciphering algorithm and the Kupenc key derived for and applicable to thesecondary layer. The WTRU may be configured to associate the addedand/or transferred DRB(s) to the MAC instance associated with thesecondary layer. For example, any user plane data for the correspondingbearer may be transmitted using a logical channel associated with theMAC instance for the secondary layer. Similar techniques may be appliedfor moving an SRB between layers as is described for moving DRBs betweenlayers.

If the reconfiguration indicates that at least one DRB isre-associated/moved from a first layer (e.g., a primary layer) to asecond layer (e.g., a secondary layer) or vice-versa, the WTRU may beconfigured to re-establish PDCP for the concerned DRB, re-establish RLCfor the concerned DRB, resume use of the concerned DRB if it had beensuspended (e.g., in case of re-establishment), and/or the PDCP entityassociated with the DRB may be configured to handle retransmissions ofunacknowledged PDCP SDUs (e.g., based on a PDCP status report).

Mobility of radio bearers at a given layer may apply current securityupdate mechanism. For example, if layer-specific security is applied atthe WTRU, depending on the control/user plane architecture, applying asecurity update may result in the KEY change operation being a functionof a change in the RRC connection and MAC instance. For example, the keymay be changed when both the RRC connection and the MAC instance ischanged to a different eNB (e.g., at either mobility at the macro layerand/or ay the small cell layer). In an example, the mobility of a radiobearer across layers may result in the bearer maintaining the samesecurity context. For example, if macro layer-specific security isapplied, depending on control/user plane architecture, the KEY changeoperation may be a function of a change in the RRC connection and thetype of RRC connection (e.g., whether it is primary/macro orsecondary/small cell layer). For example, the key may be changed for amoved bearer when the RRC connection associated with the macro cell ischanged to a different eNB, but not otherwise. Mobility of radio bearersmay result in applying re-keying at due to a radio bearer mobilityevent. For example, if WTRU-specific security is applied, depending oncontrol/user plane architecture, a KEY change operation may be afunction of a change in the RRC connection, a change in the type of RRCconnection (e.g., whether it is primary/macro or secondary/small celllayer), and/or a change in the MAC instance. For example, the key ischanged for the moved bearer based on any of a change in the nodeassociated with the RRC connection (e.g., from the macro cell layer to asmall cell layer or vice versa), the MAC instance being changed to adifferent eNB, and/or the like.

Examples may be described for ensuring secure communication between theWTRU and a SCeNB. The examples described herein may be applicable toarchitectures the PDCP protocol is terminated at the SCeNB for at leastone radio bearer, although the examples may be applicable to otherarchitectures as well. For example, the PDCP may be terminated in theSCeNB for one or more data radio bearers (DRBs) and/or one or moresignaling radio bearers (e.g., SRB3). For example, an SRB associatedwith a PDCP instance in the SCeNB may be configured to carry controlplane messages managing connectivity between the WTRU and the SCeNB.Control protocols for handling connectivity between the WTRU and theSCeNB may be referred to as secondary RRC. Secondary RRC may or may notbe configured to provide mobility for the connection between the WTRUand the SCeNB.

The peer PDCP entities in the WTRU and SCeNB may employ one or moresecurity keys. For example, the peer PDCP entities in the WTRU and SCeNBmay utilize K_(RRCint) ^((s)) and K_(RRcenc) ^((s)), for example forintegrity protection and ciphering of secondary RRC messages betweenSCeNB and WTRU, respectively. The peer PDCP entities in the WTRU andSCeNB may utilize K_(UPenc) ^((s)) for ciphering of user data (DRB)transferred between the SCeNB and WTRU.

Examples for deriving the above security keys are described. In anexample, the same keys as are used in MeNB may be used at the SCeNB andthe BEARER calculation may change. For example, one or more securitykeys applied between the WTRU and the SCeNB may be identical to one ormore security keys applied between the WTRU and the MeNB. For example,the same security keys may be used for the same purposes at each of theMeNB and the SCeNB. The WTRU may apply the same security key for anyradio bearer regardless of which MAC instance (or serving site/layer)the radio bearer is mapped to.

To enable the reuse of the security keys without compromising security,the 5-bit BEARER parameter used as input for the ciphering operation maybe different for any pair of radio bearers configured for the WTRUregardless of whether the corresponding MAC instances (or servingsites/layers) are the same or not. For example, RBs associated withdifferent layers may be assigned different RB identities, including forsignaling radio bearers. In an example, a different 5-bit beareridentity input parameter (e.g., BEARER) may be used for ciphering thanthe configured RB identity parameter. For example, the 5-bit beareridentity input parameter used for ciphering may be selected based on theRB identity and the identity of the layer that the bearer is associatedwith. For example, the BEARER parameter may be set to the RB identity ifthe bearer is associated with the MeNB, and set to the RB identity+16 ifthe bearer is associated with the SCeNB. In another example, the BEARERparameter could be set to the sum of the RB identity and a layeridentity (e.g., which may take different values depending on whether thebearer is associated with the MeNB or SCeNB). In another example, theBEARER parameter could be set to the RB identity if the bearer isassociated with the MeNB, and set to the RB identity+31 if the bearer isassociated with the SCeNB.

In an example, to enable security key reuse without compromisingsecurity, the 32-bit COUNT parameter used as input for cipheringoperation may be configured to be different for any pair of radiobearers configured for use for the WTRU. For example, the COUNTparameter may be different for each bearer regardless of whether thecorresponding MAC instances (or serving sites/layers) are the same ornot. As an example, the WTRU may utilize a 32-bit COUNT input parameterfor ciphering that is different than the COUNT of the PDCP entitycorresponding to the radio bearer on which data is being ciphered. Forexample, the COUNT input parameter may be selected as a function of theCOUNT of the PDCP entity corresponding to the radio bearer on which datais being ciphered and another parameter that is indicative of whichlayer the RB is associated with. For example, the COUNT parameter couldbe set to the PDCP COUNT associated with the PDCP entity of the radiobearer if the bearer is associated with the MeNB, and if the bearer isassociated with the SCeNB the COUNT value may be set to the COUNT of thePDCP entity+an offset. For example, the offset may be 2³¹−1. In anotherexample, the COUNT parameter could be set to the sum of the COUNT forthe corresponding PDCP entity for the bearer and of a layer identity(e.g., which may take different values depending on whether the beareris associated with the MeNB or SCeNB). In another example, the COUNTparameter may be set to the sum of the COUNT for the corresponding PDCPentity, the RB identity, and a layer identity (e.g., or some otherfunction other than a sum based on those parameters). In anotherexample, the COUNT parameter may be set to the COUNT value of the PDCPentity for the bearer if the bearer is associated with the MeNB and setto the sum of the COUNT value of the PDCP entity for the bearer+RBidentity if the bearer is associated with SCeNB.

The SCeNB may obtain the relevant keys directly from the MeNB throughbackhaul signaling (e.g., over X2bis interface) prior to and/or duringconfiguration of a secondary layer. In an example, the SCeNB may obtaina single KeNB key from the MeNB and derive the different keys forciphering and integrity protection based on KeNB. In this example, theKeNB key used by the SCeNB may be identical to the KeNB key used by theMeNB.

The SCeNB may use different keys than the MeNB. In an example, asecurity key applied between the WTRU and the SCeNB may be differentthan a security key applied between the WTRU and the MeNB for the samepurpose (e.g., ciphering of DRBs, ciphering of SRBs, integrityprotection of SRBs, etc.). The WTRU may be configured to concurrentlyapply two sets of security keys. A first set of keys (e.g., K_(UPenc),K_(RRCint), K_(RRCenc), etc.) may be applied to radio bearers mapped tothe MAC instance corresponding to the MeNB while one or more keys from asecond set of keys (e.g., K_(UPenc) ^((s)), K_(RRCint) ^((s)),K_(RRCenc) ^((s)), etc.) may be applied to radio bearers mapped to theMAC instance corresponding to the SCeNB.

For example, the WTRU may be configured to derive the keys used forradio bearers associated with the MeNB and the keys used for radiobearers associated with the SCeNB using the same KeNB. For example, theWTRU may derive the MeNB set of keys (e.g., K_(UPenc), K_(RRCint),K_(RRCenc), etc.) using a first set of algorithm type distinguisher(e.g., RRC-enc-alg, RRC-int-alg, UP-enc-alg), and the WTRU may derivesthe SCeNB set of keys (e.g., K_(UPenc) ^((s)), K_(RRCint) ^((s)),K_(RRCenc) ^((s)), etc.) using a second set of algorithm typedistinguishers (e.g., RRC-enc-alg^((s)), RRC-int-alg^((s)),UP-enc-alg^((s))).

In an example, the WTRU may be configured to derive a value KeNB^((s))(e.g., for deriving keys associated with bearers corresponding to theSCeNB) from KeNB (e.g., which is used for deriving keys associated withbearers corresponding to the MeNB). For example, the WTRU may maintaintwo currently active keys (KeNB and KeNB^((s))) for the primary andsecondary layers, respectively. Based on the key KeNB^((s)) the WTRU mayderive one or more of the second set of keys associated with bearerscorresponding to the SCeNB (e.g., K_(UPenc) ^((s)), K_(RRCint) ^((s)),K_(RRCenc) ^((s)), etc.). Upon initial configuration of a secondarylayer, the WTRU may derive the key KeNB^((s)) from the currently activeKeNB key used in the primary (macro) layer.

The derivation of KeNB^((s)) from KeNB may be performed based on ahorizontal key derivation algorithm, for example based on the physicallayer identity/physical cell identity (PCI) and the frequency EARFCN-DLof a serving cell of the secondary layer as indicated in the receivedreconfiguration message that configured the secondary layer. In anexample, the derivation may be performed based on a vertical keyderivation algorithm. For example, a vertical key derivation may beperformed if the reconfiguration message includes a nextHopChainingCount(NCC) parameter and if this parameter is different from a NCC associatedwith KeNB. The NCC associated with KeNB^((s)) may thus be different fromthe one associated with KeNB.

At the network side, the MeNB may derive the value of KeNB^((s)) fromKeNB and provide KeNB^((s)) to the SCeNB through backhaul signaling inpreparation of the configuration of the secondary layer. The MeNB maystore KeNB^((s)) for further key derivation in subsequentreconfigurations.

In an example, KeNB^((s)) may be derived based on the parameter UL NASCOUNT^((s)). For example, the WTRU may derive the KeNB^((s)) key from anadditional UL NAS COUNT^((s)) used for the purpose of key derivation inthe secondary layer. For example, the UL NAS COUNT^((s)) may be derivedby applying an offset to the UL NAS COUNT of the primary layer. Forexample, in order to derive the KeNB^((s)) key, the UL NAS COUNT may besubstituted with (UL NAS COUNT+offset) where offset may be large enoughto prevent the reuse of UL NAS COUNT values. In another example, the ULNAS COUNT^((s)) may be derived from the UL NAS COUNT of the MeNB bypadding the 24 bit internal representation of UL NAS COUNT with an8-bits sequence (e.g., that is not simply 8 zeros in the mostsignificant bits). In another example, the additional UL NAS COUNT^((s))may be derived by applying some transformation function to the UL NASCOUNT of the MeNB. For example, UL NAS COUNT^((s)) may be set to 2×ULNAS COUNT+0 or 2×UL NAS COUNT+1, etc. In another example, the KeNB ofthe MeNB layer may be derived using (2×NAS count+0) while the KeNB^((s))of the SCeNB layer may be derived using (2×UL NAS COUNT+1). In anotherexample, the UL NAS COUNT of the MeNB and the UL NAS COUNT^((s)) of theSCeNB may be set to the sum of the UL NAS COUNT and of a layer identity(e.g., which may take different values depending on whether the beareris associated with the MeNB or SCeNB). While these examples of anadditional UL NAS COUNT^((s)) calculation are expressed in terms of ULNAS COUNT, similar examples for deriving UL NAS COUNT^((s)) may beexpressed in terms of DL NAS COUNT.

In an example, KeNB^((s)) may be derived from an additional parameterKasme^((s)). For example, the WTRU may derive the KeNB^((s)) key from anadditional key (e.g., Kasme^((s)) key) used for the purpose of keyderivation in the secondary layer. The Kasme^((s)) key may be stored atthe MME and may be derived at both the UE and MME using a method similarto the method used for deriving Kasme. The WTRU may maintain anadditional NH^((s)) key and NCC^((s)) parameter for the purpose ofvertical key derivation of KeNB^((s)). At the network side, in additionto the NH and NCC pair used for the purpose of KeNB derivation, the MMEmay provide a target eNB an additional NH^((s)) key and NCC^((s))parameter. Upon a reconfiguration involving a change of MeNB, the WTRUmay be provided with both NCC and NCC^((s)) parameters and update its NHand NH^((s)) keys accordingly. The NH^((s)) key may be updated even ifnot used for deriving a KeNB^((s)) key.

Kasme^((s)) may be derived in several ways. For example, the WTRU mayderive Kasme^((s)) from an additional authentication vector used for thepurpose of key derivation in the secondary layer. As an example, theWTRU may receive an additional random number (e.g., RAND^((s))) and anadditional authentication number (e.g., AUTN^((s))) from the MME duringthe authentication and key agreement (AKA) procedure. The WTRU then usesthe RAND^((s)) and the SQN^((s)) included in the additional AUTN^((s))to generate an additional (CK^((s)), IK^((s))) pair, which the WTRU maythen use for the generation of the additional Kasme^((s)). The MME mayalso send to the WTRU an additional KSI^((s)) (Key set identifier) forexample as part of the NAS security mode command message.

In an example, the WTRU may use a “fake” or virtual serving networkID^((s)) (SN ID^((s))) or a secondary SN ID^((s)) to derive theadditional Kasme^((s)). For example, the WTRU may receive the additionalSN ID (e.g., SN ID^((s))) from the network (e.g., MME). In an example,the WTRU may generate the additional SN ID (e.g., SN ID^((s))) and maycommunicate the additional SN ID (e.g., SN ID^((s))) to the network. Inan example, the WTRU and the network may independently generate theadditional SN ID (e.g., SN ID^((s))), for example based on pre-establishrules or algorithm).

In an example, the WTRU may execute an additional AKA procedure (e.g.,AKA^((s))) with the MME. The additional AKA procedure may be asimplified version of the existing AKA procedure where the WTRU maycompute the additional CK^((s)) and IK^((s)) and may skip thecomputation of the RES (e.g., response to authentication challenge). TheWTRU may then use the additional CK^((s)), IK^((s)) for the generationof the additional Kasme^((s)). The MME may also send to the UE anadditional KSI (e.g., KSI^((s))) for generating the additionalKasme^((s)).

Upon transition from EMM-IDLE to EMM-CONNECTED, when the WTRU alreadyhas been configured with two Kasme keys (e.g., Kasme for MeNB andKasme^((s)) for SCeNB), the WTRU and the MME may coordinate the use oflayer specific Kasme a variety of methods. For example, the WTRU mayinclude two KSIs in the initial NAS message (e.g., service requestmessage). The WTRU may indicate the mapping of the KSI to eNB layer inthe initial NAS message. If the mapping of KSI to layer is notindicated, the WTRU may subsequently determine which KASME is mapped towhich eNB layer (e.g., which KASME is used to derive which KeNB at theMME), for example by doing a “blind matching” of the KeNBs. Uponreception of the AS security mode command (e.g., an RRCSecurityModeCommand message) from the eNB that the WTRU has connectionto, the WTRU may derive two KeNBs and the associated RRC integrity keysusing the two layer specific KASME(s) identified by the two KSI includedin the initial NAS message. The WTRU may iteratively verify theintegrity of the RRC security mode command message by using the RRCintegrity key(s) derived from each of the two KeNB. The WTRU mayconsiders the KeNB used to generate the RRC integrity key used tosuccessfully verify the integrity of the AS security mode command as theKeNB assigned by the MME to the eNB that the WTRU has a current RRCconnection to. Similarly, the WTRU may determine the KASME being used bythe MME to generate NAS integrity and ciphering key using a “blindmatching” principle for the first NAS message received after the servicerequest procedure. For example, the WTRU may perform “blind matching” todetermine the Kasme association to eNB layer even if WTRU indicates aKSI mapping to eNB layer initially in the service request message.

In an example, the WTRU may include one KSI in the initial NAS message,for example a service request message. For example, both the WTRU andthe network may assume the KSI is for the MeNB layer. In anotherexample, both the WTRU and the network may assume the KSI is the onethat maps to the SCeNB layer. In an example, both the WTRU and the corenetwork may assume the KSI maps to the eNB layer the UE has an RRCconnection to. In an example, the network may explicitly signal to theWTRU the mapping for of the KSI t appropriate eNB layer. A new procedure(e.g., a new NAS procedure) may be executed between the core network andthe WTRU to establish the mapping of KSI to eNB layer. The MME maytrigger the execution of this procedure. In an example, the WTRU mayderived the Kasme mapping to eNB layer from the AS security mode commandmessage.

Upon subsequent reconfiguration involving a mobility event (and/or whenthe mobilityControlInfo IE is included in the message) when the WTRUalready maintains two sets of currently active keys derived from KeNBand KeNB^((s)), the WTRU may derive new keys for the primary layer, thesecondary layer, or both, according to one or more methods.

In an example, the WTRU may maintain an indication of the most recentlyderived key (e.g., which may correspond to either KeNB or KeNB^((s))).The most recently derived key may be used as a basis for deriving a newkey KeNB* or KeNB*^((s)) upon a reconfiguration. After derivation of anew key during a subsequent reconfiguration procedure, the result of thederivation may become the new most recently derived key. If thereconfiguration involves derivation of two new keys (e.g., one for eachlayer), a subsequent (e.g., second) new key may be derived from a firstnew key. The order of key derivation may be indicated in thereconfiguration message or be pre-defined (e.g., primary layer first orsecondary layer first, etc.). The WTRU may store the most recentlyderived key even if the corresponding layer for this key is removed in asubsequent reconfiguration. At the network side, the MeNB may also storetwo keys KeNB and KeNB(s) and an indication of which is the mostrecently derived key between the two.

Upon a reconfiguration such as reconfiguration due to mobility in thesecondary layer, the MeNB may derive the new key KeNB*^((s)) from themost recently derived key, and provide the value of KeNB*^((s)) to thetarget SCeNB. Upon a reconfiguration involving mobility in the primarylayer but not the secondary layer, the MeNB may derive the new key KeNB*from the most recently derived key and provide the value of KeNB* to thetarget MeNB and/or target SCeNB. Upon a reconfiguration involvingmobility in both the primary and secondary layers, the MeNB may derivefirst a new key KeNB* from the most recently derived key and then derivea new key KeNB*^((s)) from KeNB*. The MeNB may provide the values ofKeNB* and KeNB*^((s)) to the target MeNB and the target MeNB may providethe values of KeNB*^((s)) to the target SCeNB. The new most recentlyderived key in this case may be KeNB*^((s)).

In an example, upon a reconfiguration involving mobility in the primarylayer, the WTRU may derive a new key KeNB* from its currently activeKeNB key, and upon a reconfiguration involving mobility in the secondarylayer, the WTRU may derive a new key KeNB*^((s)) from its currentlyactive KeNB^((s)) key. Thus, either or both of the currently active KeNBkey and/or KeNB^((s)) key may be used as a basis for further keyderivation depending on which layer(s) is (are) involved in the nextreconfiguration. The same principle may be used at the MeNB for thederivation of new keys KeNB*^((s)) and/or KeNB*.

In an example, the WTRU may activate the SCeNB layer AS security whenSRB1 is established (e.g., toward the MeNB) and prior the establishmentof SRB2. In another example, the WTRU may activate the SCeNB layersecurity after SRB2 is established. As part of the SCeNB AS securityactivation, the UE may derives KeNB^((s)) and the corresponding set ofsecurity keys (e.g., K_(UPenc) ^((s)), K_(RRCint) ^((s)), K_(RRCenc)^((s)), etc.) using one or more of the methods described herein.

The processes described above may be implemented in a computer program,software, and/or firmware incorporated in a computer-readable medium forexecution by a computer and/or processor. Examples of computer-readablemedia include, but are not limited to, electronic signals (transmittedover wired and/or wireless connections) and/or computer-readable storagemedia. Examples of computer-readable storage media include, but are notlimited to, a read only memory (ROM), a random access memory (RAM), aregister, cache memory, semiconductor memory devices, magnetic mediasuch as, but not limited to, internal hard disks and removable disks,magneto-optical media, and/or optical media such as CD-ROM disks, and/ordigital versatile disks (DVDs). A processor in association with softwaremay be used to implement a radio frequency transceiver for use in aWTRU, UE, terminal, base station, RNC, and/or any host computer.

What is claimed:
 1. A method for a wireless transmit receive unit(WTRU), the method comprising: the WTRU establishing a radio resourcecontrol (RRC) connection, wherein the RRC connection is common betweenat least a first medium access control (MAC) instance associated with afirst serving site and a second MAC instance associated with a secondserving site, and the RRC connection utilizes a distributed controlplane comprising a first RRC control entity at the first serving siteand a second RRC control entity at a second serving site; the WTRUreceiving an RRC connection reconfiguration message, wherein the RRCconnection reconfiguration message comprises a configuration for theWTRU to add or modify a data radio bearer (DRB) that is split betweenthe first and second MAC instances; the WTRU receiving first dataassociated with the DRB from the first serving site via the first MACinstance; and the WTRU receiving second data associated with the DRBfrom the second serving site via the second MAC instance.
 2. The methodas in claim 1, wherein the DRB is split below a packet data convergenceprotocol (PDCP) layer.
 3. The method as in claim 1, wherein the firstRRC entity at the first serving site corresponds to primary RRC entityat a macro cell.
 4. The method as in claim 3, wherein the second RRCentity at the second serving site corresponds to supplemental RRC entityat a small cell.
 5. The method as in claim 1, wherein the first RRCentity supports at least one control plane function that is notsupported by the second RRC entity.
 6. The method as in claim 1, whereina single RRC entity at the WTRU is configured to coordinate with each ofthe first and second RRC entities.
 7. The method as in claim 1, whereinthe first serving site corresponds to a first type of radio access nodeassociated with a first cell type and the second serving sitecorresponds to a second type of radio access node associated with asecond cell type.
 8. A wireless transmit receive unit (WTRU) comprising:a transceiver, and a processor configured to: establish a radio resourcecontrol (RRC) connection, wherein the RRC connection is common betweenat least a first medium access control (MAC) instance associated with afirst serving site and a second MAC instance associated with a secondserving site, and the RRC connection utilizes a distributed controlplane comprising a first RRC control entity at the first serving siteand a second RRC control entity at a second serving site; receive, viathe transceiver, an RRC connection reconfiguration message, wherein theRRC connection reconfiguration message comprises a configuration for theWTRU to add or modify a data radio bearer (DRB) that is split betweenthe first and second MAC instances; receive, via the transceiver, firstdata associated with the DRB from the first serving site via the firstMAC instance; and receive, via the transceiver, second data associatedwith the DRB from the second serving site via the second MAC instance.9. The WTRU as in claim 8, wherein the DRB is split below a packet dataconvergence protocol (PDCP) layer.
 10. The WTRU as in claim 8, whereinthe first RRC entity at the first serving site corresponds to primaryRRC entity at a macro cell.
 11. The WTRU as in claim 9, wherein thesecond RRC entity at the second serving site corresponds to supplementalRRC entity at a small cell.
 12. The WTRU as in claim 8, wherein thefirst RRC entity supports at least one control plane function that isnot supported by the second RRC entity.
 13. The WTRU as in claim 8,wherein a single RRC entity at the WTRU is configured to coordinate witheach of the first and second RRC entities.
 14. The WTRU as in claim 8,wherein the first serving site corresponds to a first type of radioaccess node associated with a first cell type and the second servingsite corresponds to a second type of radio access node associated with asecond cell type.
 15. A network node comprising: a transceiver, and aprocessor configured to: establish a radio resource control (RRC)connection with a wireless transmit receive unit (WTRU), wherein thenetwork node corresponds to a first serving site for the WTRU, the RRCconnection is common between at least a first medium access control(MAC) instance of the WTRU associated with the first serving site and asecond MAC instance of the WTRU associated with a second serving site,and the RRC connection utilizes a distributed control plane comprising afirst RRC control entity at the network node and a second RRC controlentity at a second serving site; send, via the transceiver, an RRCconnection reconfiguration message to the WTRU, wherein the RRCconnection reconfiguration message comprises a configuration for theWTRU to add or modify a data radio bearer (DRB) that is split betweenthe first and second MAC instances; send, via the transceiver, firstdata associated with the DRB to the WTRU, the first data beingassociated with the first MAC instance; and send, via the transceiver,second data to the second serving site for delivery to the WTRU, thesecond data being associated with the DRB and with the second MACinstance.
 16. The network node as in claim 15, wherein the DRB is splitbelow a packet data convergence protocol (PDCP) layer.
 17. The networknode as in claim 15, wherein the first RRC entity at the network nodecorresponds to primary RRC entity at a macro cell.
 18. The network nodeas in claim 15, wherein the first RRC entity supports at least onecontrol plane function that is not supported by the second RRC entity.19. The network node as in claim 15, wherein the first RRC entity isconfigured to control one or more mobility aspects of the WTRU.
 20. Thenetwork node as in claim 15, wherein the network node corresponds to afirst type of radio access node associated with a first cell type andthe second serving site corresponds to a second type of radio accessnode associated with a second cell type.